Did quite a bit of research on these recently, so I might be able to help. First though, I apologize for the novel I'm about to write.
The short for is that it really depends on what you're looking for in a system. Both systems have their ups and downs, and they don't do all the same things in the same ways. We ended up getting the chatterbox system, as it seemed to come closer to meeting the list of priorities we had. On the other hand, we were able to find clearer internet reviews of the Scala Rider G4. In any case, I'll list off some of the things that Myself and my riding buddies had in mind when we went shopping for headsets, and maybe Gpmo will chip in with anything else he remembers at some point.
1.) Are you concerned with having Full Duplex communications?
(this is where both/all parties are able to speak at once, rather than one person keying up to transmit at a time) Scala will have this, Chatterbox won't. However, even though the Scala has it, it gets less useful as you increase the number of riders. For only 2 riders, its perfect. At 3 riders, it will take over one of your bluetooth device channels, so you can't connect as many bluetooth devices to it. Also, at 3 riders, it works differently. There will be a channel A and a Channel B, each headset can only connect to one other headset per channel. So Riders 1&2 connect to each other through channel A, Riders 2&3 connect to each other through channel B. This means that everyone can hear rider 2, and rider 2 can hear riders 1 and 3, but riders 1 and 3 can't hear each other.
2.) How many people will be in your riding group?
Scala will handle up to 4 total, and at 4 riders, you can once again do full duplex. Sort of. Riders 1&2 connect via channel A, Riders 3&4 also connect Channel A seperately, then Riders 1&3 also use channel B to connect to each other, while riders 2&4 connect on another channel B as well. Then, when everyone wants to start talking, there's a series of buttons to hit, which eventually opens up a full intercom mode. Sorry I couldn't clarify the Scala connections any better, but they explanations in the manual aren't great, although it IS possible to puzzle it out using the diagrams. Chatterbox will handle pretty much as many riders as you can possibly cram together. There are a bunch of channels, but everyone just switches to the same channel, and then when one person talks, everybody hears it (as long as only one person tries talking at once.
3.)What kinds of distances do you want to be able to reach?
Scala is rated for 1/4 mile, but I haven't gotten the opportunity to test the range in practical application. Chatterbox is listed at up to 5 miles. Obviously, you won't be able to reach 5 miles through town, or arounds 6 corners up a canyon, but on a flat highway we've confirmed several miles of range, and in the canyons we still have a good spread, but haven't really tried pushing this limit.
There's a number of other concerns, obviously, but I'm feeling bad for taking up so much time already, so I'll just keep the rest handy for answering whatever questions you might have regarding your priorities. In short, the Scala Rider G4 looks like a very nice system and got positive reviews from most people we talked to, as well as being much smaller. If there were only 2 of us riding, we'd have probably picked it up. However, there are 3 of us riding together frequently right now,a nd we wanted the option of expanding to more, as several other friends are interested in getting motorcycles and joining us. In addition, we wanted the process of connecting additional riders to be simple, and to be sure that everyone could always hear whoever is in front giving warnings regarding road hazards, fuel stops, and whatever else we all need to know. We also didn't want to be concerned about getting far enough out of range to lose somebody out of the communication system and not realize it.
Ok, again, sorry for the book, and I'll try to be more brief with any followup. Or, Just PM me, and I can answer more via email or phone.