My main riding partner Festar and I both have Sena 20's.
Paired together we do pretty well, range is about half a mile on flat ground out in the country where there is little electronic interference.
Pairing three 20's often introduces spurious electronic noise and clicking, you want to make sure that the rider in the middle of the group is the guy everyone pairs to.
Pairing four Sena 20's is often an exercise in frustration. "Can you hear me now......? Etc, Etc, Etc. Couldn't make it work in the CycleGear parking Lot at SFO even with one of their supposed experts coaching us in the setup and pairing process
I have not had much luck with the "Group Intercom" functionality. I think it has more to do with my lack of knowledge and everyone possibly not being on the same firmware release from Sena. I'm going to try to do a Group Intercom one day during my Black Hills Roundup II in June. I'll verify everyone is on the same Firmware, that everyone has named their Sena 20 and then use my Phone to create the group and see if we can make it work.
All that said, when it is just Festar and I we really enjoy the ability to talk. I pair my Android phone to my Sena as well. Seamless and great fidelity little noise when talking to someone on the phone, they are often amazed when I tell them I'm on the bike and rolling.
I have speakers in my helmet and also have Fuze Earbuds. When I use the Speakers i wear some custom molded earplugs, the Fuze Ear Buds are also custom molded. The Fuze Buds do work better for phone, music, and conversation but after several days it is nice to switch to the other plugs.
I had the Scala G9 setup before I bought the Sena. I could get it to pair with a Sena 10, but range was quite limited and it didn't like my phone very much.
My first Sena 20 unit was not even close to water resistant. It failed and was promptly replaced by Sena. The replacement has not let me down once, 14 straight days in Alaska it rained and I was able to maintain a good connection with my riding partner on that adventure.
In my opinion, the connectivity limitations of the Sena 20 has more to do with the available Blue Tooth architecture than the Sena Units themselves.