I just bought a FX3 and it works great, I'm not sure what the difference between models are, however I can give you what i know so far.
-The Fx3 has 32 program channels and I thought that was tons, but its just enough for me, it didn't take long to fill them with what i wanted.
-The volume I wouldn't want any lower its great to haveing the juice to call crows at the start then turn down as required and those windy days seem to kill the sound.
-haven't had a chance to test remote distance yet
overall works great clear sound and is a blast to scar friends with.