I think Solo trumps the FVS2 when it comes to stealth, and the FVS2 appears to have more immediate and impressive vapor production. Talking with an owner of both gave me this impression and Vito's video does too.Armerad is definitely correct about also taking into consideration the ease with which your vaporizer will mate to glass, and the Solo seems to win there. The Solo would seem to me to have superior life on a full charge (8-12 bowls) to the two batteries which comes with the FVS2, which are supposed to be good for 1-3 bowls each, and I think 3 is pushing it. The Solo has one of the lowest, easiest learning curves of any vaporizer I've ever used - you can share it with those completely unfamiliar with it and they'll get satisfying clouds as long as they can simply inhale on a tube.
I've ordered a FVS2 out of my own rampant curiousity, with the rationalization that I'll use it for "educational reasons" alone and will only fail to sell/trade it away if I absolutely love it.