I've used SMH10 for a long time it was good but when it needed replacement I tried the updated 10s - not good at all. The 10s had so many 'teething' problems that my friends and I formed the opinion that SENA has launched it into the market not fully tested. It would fail to connect, switch off for no reason and the sound quality and range was disappointing. We returned them and upgraded to the 20s
The 20s has had several iterations of firmware upgrades and seems to be much more like the finished article. Although more expensive, it offers the great advantage of allowing intercom conversation whilst at the same time listening to satnav directions and/or music. The 10 (lesses?) versions interrupt conversation when satnav announcements are made. You may think this is a small thing but if you bear in mind how much the satnav says whilst in towns for example, or when the speed alerts are activated, then you will realise why we tended to mute the satnav and maintain the intercom.
The 20s offers the best of both worlds plus a range of other features such as a radio and voice control (admittedly not imperative but quite useful)