AMB-it is now MyLaps. MyLaps renamed the AMB DP (personal transponder), and called it an RC2... So you will see some MyLaps transponders that look like the AMB... with a MyLaps label.... These are no longer made.

The RC4 is the latest transponder. Its smaller, has removable tabs,.. and a few other fetchers that will only work with the RC4 decoder... (this isn't out yet).... Its also backwards compatible with the AMBrc & AMBrc3 decoder.