I'm running the MMpro with a 1512 1400kv motor right now. Batts are 6s1p and Rustler total weight is about 8lbs. Fan doesn't even come on, even running through grass. After the pack dumped, motor temps were at 115F and both ESC+batts at around 99F. Using Castle 4mm plugs.
I have been using the MMPro in my 808 5s/1550kv T8 motor since it was released to the public. Works just fine. Runs cool, fan barely comes on.
The only problem I have experienced is that just last week I got some servo glitching and would periodically lose steering. This was after running a 10 minute main and then bumping up to immediately run a 15 minute main. About 10 minutes in my steering started glitching. I know some units have had issues with the BEC. I am running 400oz JR servo in my buggy, so it may be drawing a bit much for it.
I put my CC External BEC on and it seems to be working fine. Regardless, the MMPro is one of the longest lasting ESC I have had in my buggy.