I've seen 2-3 MTronics low end ESC - very strange behavior from time to time. Personally I wouldn't spend money on them. I dont know of the high end stuff though.
There's a GM V8 and V12 in our club - people are very happy with them. One thing I rellay like about the GM, is that it's the cheapest ESC I've seen so far, with a 6 volt BEC. I've read somwhere that GM's not the easiest to program. But I havent tried it myself though.
Schumacher Mi5 - Sanwa MT-4 / RX-462 / KO Propo PDS-2123 - Nosram 5600 X-treme Saddle Pack - LRP SPX Zero/X12 17,5 - Nosram Stealth Touch Evolution - MAAS SPS 9250