RE: 50cc Radio and battery setup?
You need two switches and two batteries for the 921. No soft switch. The 9100 has the soft switch, however, since the batteries are connected directly to the receiver, there will be a small amount of current draw when the receiver is off. You would have to unplug the batteries from the 9100 if they sit more than a month. I like the 9100 as you have all the receivers external from the power bus, so if one fails, you have three as backup. I had a 921 receiver where one external receiver died in flight. I didn't notice it until I landed and didn't see the light on the receiver. Hope this helps.
Scott