I bought the 5720 from motorola, the downside is that they only come in pairs, but the pair is only 50 bucks or so.
One thing to be careful of with the voice activated radios, if you are driving and you have music playing it will activate the radio. This has two potential downsides:
1. Not everyone in the caravan wil like your taste in music

2. Your batteries will wear down faster due to the continuous transmission.
We had this happen on the trip to WGI this past May, for about 30 minutes we all had to listen to someone's radio in their Vette.
Mark