I'm on my 3rd Sena 20s.
Overall it's a good unit, and when it works it's just awesome....but I think it's a flawed product that could be a lot better. 4 of the 5 guys I ride with have the 20s, and group communciation is always a fucking pain...people drop off, pairings don't retain, we end up fussing with it at every stop. Annoying as fuck, everyone's technically savvy, all matching settings, firmware, they just don't play nice in a big group. Now, pairing with 1 other person? Pretty flawless, and the features rock.
The other issue I've had is a bad base on one of my units (wouldn't ever seat correctly, lost audio on one channel). Sena replaced it, the second unit worked for a while but kept locking up, requiring a hard-reset with a paper clip...replaced that one too. The 3rd unit has been good so far.
My experience is not rare, btw, here's a big thread on the 20s and a lot of people have had some niggling issues.
http://advrider.com/index.php?threads/sena-s20-experience.993790/
Would I buy the 20s again? Probably, it's so nice when it works, but I think for the $$ they charge, it's got too many bugs and the build quality isn't there.