I did a comprehensive 3 hour A/B testing of the V3, V2 and my own CIEM at my local store yesterday. However, I am not a professional or even avid reviewer/commenter, so please forgive my lack of know-how to describe what I feel, especially in the technicalities.
Before I launch into what I think of the V3, I shall preface by saying that I've been/still am, a daily user of the Heir Audio 8As. Dark, bass heavy and warm is what I have been listening to daily for coming on about 7 years now. I also own the UE Superfi.5 EBs and VE Monk IE, and have owned a lot of others in the past. I always buy and sell earphones to experiment with what I like.
I am currently using a Sony ZX300, and use a mix of hi-res and standard mp3 to test. I tested both with the 3.5mm jack.
Initially, at CanJam Singapore 2018, I was interested in the V2's because they were very different from what I had been listening to for years. What I feel about the V2's is exactly the same as what crinacle feels about them, so I'll not describe them here. However, I'll mention that the mid range is what drew me to the V2s. It was different, and while it took me a while to like them as a whole, probably due to my long-term exposure to the Heir Audio 8As, I eventually succumbed to the magic of the V2's midrange.
Another worth mentioning here is that I benefited A LOT from tip rolling. I found the M SpinFits to be the best for testing as they allow me to insert the V3 deeper than foam, hybrids or any other I've tested. The depth of insertion, too, played a part, and thus is something to keep in mind, especially since I am considering the custom version and not the universal.
V3, to me, was markedly different from the V2. I wouldn't go so far as to say they are completely different earphones, but they are certainly different enough that I could tell them apart from the moment I hit the play button. I would say that I could immediately tell that they are built from the same base, and that they did something about the tuning. The part of the tuning I felt that they touched the least, is the bass. I would say this part is close to untouched, and this is from coming from a guy who enjoyed quality(?) + quantity bass from my Heir Audio 8As.
The V3 vocals are a lot more forward sounding to me. I used Jay Chou's Qing Hua Ci to test vocals and strings. For vocals, I felt that the V3, in my mind, is probably better for the stage; I could more closely monitor my voice, and they felt more like a part of the music in terms of coherency, if that makes sense. I felt that the V2's vocals were a little far away, introducing a sort of 3 dimensional break from the instruments. Like a small, not very exciting artificial soundstage.
The gu zheng in the track, however, is what I felt was the big biggest difference. The V3 sounded very full bodied, and I found that I could almost feel the plucking of the strings from the moment the fingers touched the string till the finger leaves it. The V2 does strings exceptionally well as well, but in my honest opinion, was a little too laidback, and thus lacked the full-bodiedness of the V3.
In my 3 hours of continuous A/B, these are the two main differences I could pick out immediately. The rest are not as obvious to me, but I firmly believe that music is presented and should be judged as a whole package, but just from specific parts.
Another point I would like to raise is when trying out electronic music and J/KPop. I tried multiple tracks, and found that the V2 were not as aggressive as the V3. Actually, if I would make a sweeping judgement on the difference between the two, the V2 is not as aggressive as the V3 is what I would say.
Something that I noted is that when I did A/B with my Heir Audio 8A against the V3, then the V2, I found the change between the V3 and the 8A to be less jarring. Again, take that as you will.
I will go back to test them again soon to more correctly make a decision as to whether I want the V3 in the end. For now, I am still hopeful that the V3 will remain on my wishlist. They are different, for sure, but I do believe that they appeal to almost entirely different crowds.
If anyone is interested in wanting to know specific differences, I try my best to do so in my next testing session. I will be making a decision as to whether I want the V3 or not by the 13th, latest.
Another thing, for anyone who haven't seen the IPX connector and have doubts about the build, don't worry. The connector is the best IEM connector I have seen to date. Also, the V3 universal shell seems a lot smoother and smaller than the V2 universal.
P.S. When I asked the staff, he mentioned to me that some guy recently got the custom V3, tested, and didn't mention anything about the difference between the display(V2) unit and what he got. Also, another shop's staff told me that the V3 benefits a lot from burn-in. I believe in brain- burn in, but not so much of the drivers' burn in. I hope this information helps as well.
