FASST-C1 vs FASST-C2
#1

I notice that the 4PK uses a newer standard of Futaba's FASST, they call it FASST-C2 in the manual. To use the 4PK with older FASST receivers, FASST-C1 must be selected from the radio. I can't find anything that explains the difference though, presumably C2 is better, anybody know what the difference is?