Full disclaimer up front: This is my first plunge into TOTL IEMs, so I don't have an extensive amount of experience with other TOTL options to compare.

I have owned my V14 for a bit less than a year now, and I have been using it basically daily for long periods of time (6+ hours at a time). At this point, I feel confident in my opinion on this IEM.

The QDC V14 is sonically awesome. I have not heard this IEM choke on anything I have played through it. EDM, Prog metal, Thrash, Orchestral pieces, Swing Jazz, and whatever else I fancy poses no technical issues for the V14. Every instrument is played back clearly and distinct from other similar instruments, so the sound image is exceedingly precise. Tracks involving 3 electric guitars and a violin playing simultaneously have played havoc on lower budget audio gear I have used, and the V14 handles these songs flawlessly. This IEM represents the technical capabilities of the TOTL without disappointment for me.

The above is the reason why I put up with the many problems the V14 comes with.

First is comfort. When I was researching what I wanted to choose as my entry into the TOTL world, I was assured that the V14 was quite comfortable by everyone who reviewed it. I had the exact opposite experience. The body of the IEM has a little wing at the top that I think is supposed to interact with the antihelix of the pinna for some reason, and that wing is the reason that I will not purchase any further IEMs designed by QDC until it is fixed. On this supposedly universal IEM, that shape severely interferes with fitment on anyone who doesn't have a specific pinna shape QDC had in mind. If that wing were not there, I would have no issue with the shell; as it stands I get sharp pain in a few minutes if I don't use the custom tips I ordered to alleviate this problem out of necessity. This is a huge miss on the design side by QDC, especially since it's on the side no one will see.

Second, I had a number of minor QC issues arise on my model. The left 2 pin socket unit is slightly too loose, which lead to me nearly losing the left unit at one point. The nozzle of one of my units fell off the shell because the resin was not properly formed around it. The glue holding the wax filters in place on the nozzle failed in a few months. The IEM seems filled up with some sort of damping material that is preventing air flow through the venting hole, and this causes air pressure problems when in use (QDC claims the V14 is vented, meaning my unit is either defective or they are lying about this). I understand no company is going to be perfect with QC, but this is a shocking lack of attention given to fit and finish for this price bracket. I expect TOTL IEMs like this to be near perfect every time.

Third is the tuning. There is a bit of a harsh peak at 8.8k to my ear that adds too much sibilant bite to most tracks. It's not a big peak (I EQ'd that down about 2 dB and it's no longer a problem) so I put that down to my HRTF not favoring that. However, QDC made a strange decision with the pinna gain compensation. Instead of gently building an upward curve to somewhere near 3k, they plateau'd the curve at 2k and scooped out some of the response from 2k to 3.1k, and this causes a strange issue with guitars and female vocals where the rest of the track will sound right at head level, but the guitars and vocals will sound vertically depressed. I think this is not just an HRTF problem because Precogvision also noted this dip in the middle of the sound image, meaning others are also experiencing this. This quirk in the tuning marrs what is otherwise an outstanding presentation of sound.

While I enjoy the V14 I have arrived at, the process was not exactly what I had hoped for from a TOTL offering. I really hope this is not indicative of the industry as a whole, the prices being asked for should guarantee an excellent experience the entire way through IMO.

These headphones are quite something. I have been using them for about a month now, and I have no plans on selling or switching at this point. Note: I am writing my thoughts on these after having swapped the pads for Brainwavz angled memory foam earpads.

Build Quality: I'm coming to these from the V-Moda Crossfade 2 Wireless, and these are relatively a step down from those. There's creaking and rattling coming from the plastic slider buttons and the headband, which is annoying when quiet music is playing, but I have stopped noticing it as much during active use. It's still a miss, and I'm on the lookout for any kind of build failure that may indicate poor quality control, but so far it's been just a minor annoyance.
I have heard complaints about the mic, so I gave it a try to see if I had the same problem. It seems that my particular unit doesn't have this same issue when using it with a smartphone, so I have nothing bad to report on that front. It is apparently not good at reducing ambient noise though, so there's something to consider.
[Edit: 3/2/2018] After some more use, I'm encountering some problems with the mic's gain. Some people can hear me fine, some others apparently can't hear me at all. I'll have to recommend that you look elsewhere if you plan on using your phone extensively while using these cans.

Accessories: Not much here, just a hard case and a thick USB 2.0 to micro USB cable. Note about the cable: It's really annoying that the micro USB port is recessed into the left driver housing. I have tested the port with different data USB cables and they all work, you just need to either find one that is narrow enough to fit or cut away enough rubber to force a fit.

Connectivity: I haven't had problems with the connectivity beyond the first day. Plugging into my computer took a while as Windows had to look around to find the drivers, but once it installed the proper drivers it functions fine. Bluetooth pairing is quick and relatively good on operational distance. From what I see, it can't handle multiple connections or anything fancy like that, but I don't have any need to do things like that, so no loss to me.
[Edit: 3/2/2018] Something interesting I found here is that the on/off switch position matters when the cans are plugged in for wired use. The manual says it doesn't matter as the cans switch off when wired, but the volume slider changes the volume when the power switch is on. Nothing else seems to function besides this though.

Comfort: These are relatively good stock. There's enough room for most peoples' ears to fit comfortably. I noticed a little chafing after a while, and it was starting to irritate me at the end of the day. Thankfully, these earpads are easy to swap out, and the angled memory foam earpads provide a huge amount of real estate for my ears, making these leagues ahead of any over-ears from V-moda (not that big a hurdle) and sufficient for continuous use over almost half a day for me. The headband is too straight as is, which makes a hotspot at the top of the head. I bent the headband until the center was curving over my head and more of the headband is touching my head now, so I don't have the hotspot problem anymore. While the outside of the headphone may feel too plasticky for my taste, the inner components seem to be quality as they survived almost as much bending as I subjected both my V-moda cans to.

Sound Quality: Now, I have heard various cans that are considered neutral in passing over the last 2 years (HD600, STAX L300, ATH-M50x, etc), but not for long enough to really acclimate to what those sound like, so my impression of what these sound like may be incorrectly framed at the moment. Listening closely, I'm surprised to hear what sounds like a slightly V-shaped response curve from these. Given that these are in AT's Sound Reality line, I was expecting a FR curve closer to neutral than what I'm hearing. The low end is slightly elevated above neutral up to ~270 Hz, at which point it dips sharply (valleying out at around 320 Hz) before rising back up to normal at 340 Hz. The mid range seems relatively normal, although I am noticing some recession in the vocal ranges. The treble has no roll-off, so we're in for the full experience here. I hear relatively small but noticable peaks throughout the treble range (notably at ~8kHz). This all comes together into a headphone that is quite bright in character without leaving the low end behind, and yet it somehow manages to not be sibilant in most cases (Metalheads, look elsewhere. These do not render distorted guitars in very pleasant ways if the mastering doesn't specifically reduce those frequencies). The big dip at 330 Hz doesn't seem to detrimentally effect music to me, in fact I tried dipping that range on an equalizer with my other cans, and it noticably improved the sound of those too. Interesting.
The clarity in the sound is extraordinary for wireless cans, in fact I hear much more detail and clarity with these than I do with my wired cans (M-100, CF2W, HE-400S, M-40x) which very much surprised me. The soundstage is wide without being obnoxiously spacious, the imaging seems accurate to me when listening to electronic music. I have heard the sound described as a hollow kind of sound, which I suppose is understandable considering, but I prefer this kind of sound to what I perceive as a bloated low mid range present in most other cans I listen to.
Overall, I really like the sound signature of these. It's not exactly neutral, but since I'm not an audio professional I'm not looking for something like that.
[Edit: 3/2/2018]: I did some A/B testing comparing 16/44.1 MP3 to 24/96 FLAC formats of the same electronic song (Mont-blanc from Tokyo Audio Waffle's Maple Mont-Blanc in particular) on these headphones, and I was surprised by the imaging precision. Sounds that I had previously perceived as just being to the left and pulsing on the CF2W were coming through as if the source was circling clockwise 6~8 inches away from my head.

Portability/Mobility: Like most AT headphones, the driver housings swivel, so that's nice. However, they are still uncomfortable to have around my neck, and since they don't compact down like the CF2W does, I'm kind of stuck with them like that. Now, I have these on normally for most of my day anyway so it's not a big issue, but it is an issue to consider. Another thing to consider is that these are semi-open (there's a small port right on top of the driver housing, which is what I think is letting air in for the driver to generate as much low end as it does), and as such is not very good at attenuating noise. I can hear cars passing and people talking while playing music at a moderate volume, which is a problem if you want to shut out the world and live in the music, but it's not so bad that it's unusable in my opinion.

Audio Technica is on to something with these headphones. If they can tighten up the build quality,flatten out the V curve a bit, and make these better at being portable headphones, I think these would be close to perfect.