I have the basic Chatterbox intercom for 2 people on one bike. It works really well and is simple to use. I have heard that the bike to bike systems Chatterbox has works well also. I have never used one but I am considering purchasing one later in the year. I have always heard good reports about Chatterbox. I belive they were the first to offer this type of equipment.
We have the pro FRS system, all I can say is it works good, sure bets honking your horn, flashing your lights, or waving your hands to get the attention of the other rider, just talk to them and then listen, not much easier than that.