This will be used for 2 things....IEM at my house to practice and to send a signal to my powered speakers when I have an event.
I've used only the Carvin, not the M2s, but...
How likely are you to expand your applications? As-is, the 2nd transmitter would let you and a bandmate each run a stereo IEM mix for rehearsals. But if you might eventually expand the system with more receivers for gigging, the 2nd transmitter is a bigger deal. (Personally, I don't mind wired for rehearsaland it's a lot cheaper that way. So if this were a system I wouldn't be gigging, I probably wouldn't drop the scratch just to expand a *wireless* IEM rehearsal system. YMMV.)
As-is, with the Carvin's one transmitter and two receivers in dual-mono mode, you could have a mono IEM mix for yourself while sending the FOH mix to one powered cab; but you'd have to daisy-chain a pass-through signal from that first cab across stage to your second powered cab.
But with the AT system's two transmitters, add a 3rd receiver, and you can drive your powered FOH cabs while still enjoying your own stereo IEM mix.
Add a 4th receiver, and you could feed both of your active FOH cabs wirelessly, while still having a stereo IEM mix for yourself. Or you could wire your FOH cabs, and instead run four custom mixes (in dual-mono mode) for bandmates. Or, you could feed your active FOH cabs w/o daisy-chain cabling, and have dual mono mixes for yourself and a bandmate.
Not going to do any of that? I'd get the Carvins, which work well and are good value. Thinking of expanding? The two-transmitter system starts to give a lot more flexibility.