The Swiss Sequential team used them at one time (c.1995). I remember it having mixed reviews, too many people talking at once or getting confused on them.
There's also people like me who hum a song the whole time - that tends to piss off the rest of the team.
I used them (radio shack) when training a pup (now a US Record and soon to be World Record holder) about a decade ago. Marginal utility in the air but we had a lot of fun with them driving to and from the DZ when we shared a couple hundred miles of Turnpike.
Bill had his permanently affixed to his Protec and looked like he was driving to 'special' school
We, the Dutch CF team, are using radios (Maxon 49SX & FX like the Swiss team used to have) for about 7 years now and we're pretty satisfied with them. You've to get used to them regarding who can speak. Only one can speak at a time. They're voice activated and we've build them into Z1 fullface helmets (without visor).
We primarily use for for giving the keys not only in rotation (instead of a whistle) but also for sequential.
The range is limited (150 ft effective) but if the separation is more than that it's bad anyway. They're also great for jumping with students.
