Honestly, S20s aren't super intuitive .. you have to do your homework on learning how to use them/set them up. Also, SENA's video how to's kind of suck.. so you really have to just tinker with them to learn how they work best.
When I ride with my wife, they work awesomely. Pair up immediately, great audio, tremendous battery life- they're worth every penny.
In larger groups,things become a bit more difficult, and I think I know why. These things run off Bluetooth- which is a great protocol for many purposes, but it can have difficulty in areas with really high channel saturation. Almost everyone in a group ride has a smart phone and BT is usually enabled on most of them. Then you factor in line-of-site, and that further complicates the chain.
So, what you end up having is much like going to a crowded dr's office, full of crying children, and trying to have a conversation with several people 10-30 feet away. The sena units have to filter a ton of cross chatter on the protocol level, which is made more difficult by folks not all being on the same software revision, etc.
They can be finicky, i totally agree.. but it think most of the issues are unintentionally created by the people using them, to be honest