OK now that i've had a few weeks with my hippo VBs i can post more about them, i've been meaning to do it but those IEMs didnt seem to get a lot of interest anymore.
I would second everything miow has said above, except that the sibilance/treble harshness was so bad for me (actually hurting my ears very fast) that i found absolutely mandatory to throw some foam in the canals. The result : close to no more harshness, still some sibilance (but nothing above average at all), and i dont feel that the great soundstage has been affected too much (probably narrowed just a little), the bass might have been dampened just a tiny barely noticeable little bit, but it was REALLY worth it.
The overall signature is really balanced, although with the right tip fit, the sub-bass rumble (sometimes reverberating with great effect), when the music calls for it, can be a little bit too much for me on an otherwise delicate song, and sometimes overpowers the mid to upper bass. Note that the bass NEVER affects the other ranges, mids stay absolutely clear at all time (even with a rumbling, thundering sub-bass) which is pretty impressive... no midbass bloat at all, but i sometimes feel that the sub-bass can overpower the mid-bass but this only happens on a few (mostly hip-hop style) songs and i found a way to counter it : using the tips one size below what fits perfectly (for me, that would be S instead of M), it cuts a LOT of that rumbling sub bass but still retain some of it and doesnt affect the midbass at all. I admit i dont do it often as having that great rumbling sub-bass on energetic songs is quite a lot of fun most of the time.
So yeah, those are definitely IEMs to recommend blindly to anyone that isnt too sensitive to treble harshness and likes a lively, "balanced with big sub-bass" sound signature along with a great soundstage. Those who are treble sensitive will definitely have to do the foam mod, and it will probably be a deal breaker for some to mandatorily have to mod a pair of earphones before being able to listen to them. Also, those who like a refined and ultra-detailed treble (and upper-mids) will be disappointed.
I've had a few amazing, quasi cinematic, musical experiences with the VBs in my bed while listening to some albums. It was mainly some real quiet jazz (such as miles davis kind of blue) and "rock" (such santana's black magic woman) and also other great smooth african music, that i was listening as a mean to lullaby myself to sleep... it actually kept me fully awake (for HOURS even though i was really tired), in an almost extatic state. Its the first time i have this kind of experience with earphones, so i can definitely say that the VBs are the best i've owned so far (although... i havent owned many)
So yeah, thanks dfkt for the recommendation, although i feel the quest is not over for me yet...
EDIT: now that i own a an overall much more neutral phone (cyclone pr1 pro), i can better judge the VB sound signature : i used to think that the mids were pretty neutral ( i had only owned senn IEMs & headphones before, & the pl21!), now the warmth is much more obvious to me (something that i actually like most of the time, even though it's nice to have something neutral too)... I'm not sure about the terminology, but there is definitely some (very reasonable) upper bass (or is it midbass?... it doesnt affect the "regular" basslines) hump that is partly responsible for the overall warmful presentation, although some other (very reasonable, again )coloration(?) is also contributing to the warmth that can be felt all across the sonic range. Note that this is a plus for me about 75% of the time. And i'm gonna try those special burn-in recipes, but even with all the listening i've done so far, the treble (and higher mids) are still pretty rough and as a result not so defined. Maybe i just got a bad batch...