I don't know about you, but I know carrying decoys, a gun, caller, and everything else can get pretty tiring in a day. I think the Prey Master would be a bit lighter /ubbthreads/images/graemlins/smile.gif I looked at Bass Pro and they did not have the JS Power Pro Convert a Caller listed, but maybe if you gave them a call. Mine ran around 110 bucks. If you are worried about volume, they did have the Prey Master Power Pro combo unit for 199 though.
I've found that even with an electronic caller, if you use a hand call ( I actually use a couple or three - two different crow calls and a hawk screamer) I get better results at calling them in.
I have to go with Crapshoot on this one. If you can't get the Power Pro, I would go with the Prey Master. Once the crows show up they will make their own music and you wont need the caller anyway, you'll be too busy shooting /ubbthreads/images/graemlins/smile.gif