First question is what exactly do you want from it?
Scala / Sena are the major competitors, you'll have users of both voicing their one is better (I'm on the Sena side for the record). If your requirements are connecting to phone/GPS and other basic devices, then either should do the job.
If you want to connect to other people then it's more tricky. Compatibility between brands is advertised but limited (can't have as many devices in comms as if everyone had the same brand) and I haven't really seen it working in a practical demonstration yet. A group I'm in has a number of Sena units, to the point that the major issue with connecting is pairing with the wrong people as most try it at once. ie, instead of the person you want, you get someone else around the corner
I use Sena a lot, no problem. Depending again on your requirement, the 10 range may be perfectly fine, and cheaper than the 20... I've been using 10 for the last couple of years, have a 10R on my helmet permanently installed, and a 10B to install on other helmets.
One note on the 20S is that a lot of early units had problems that should now be fixed with updated firmware, but unsure what, if any, problems still exist. Not too surprising with any new product from anyone...
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