My first MMM simply stopped working after a few hours of use, it died after a lot of hard braking in a ~16 pound Muggy with the brakes at the default 50%. I set my new one to 30% (still really powerful) and it's got around 20 hours on it without a hitch, but every RC I own is broken in some way so I can't punish it more.
I had my first MM die after being run in the snow, drug through the snow when my velcro came loose, completely submerged when my old radio glitched out, and running through tons of puddles. Running it on 12 cells popped a FET and they replaced it for free, all the water abuse didn't even bother it. My next MM would work with my CC 5700 motor but nothing else, but it was the replacement from the first one that went out so I had to pay $45 to fix it. The 3rd MM I've had go bad was one that was given to me after a firmware upgrade bricked it, and they replaced it for free.
Every failure I've had other than the firmware problem could be linked to my abuse of the ESC and they could have made me pay for the repairs but I only had to fix 1 which was well out of it's warranty period. Since then I've bought 3 more MMs and they all still work (2 are for sale

) I'm building an offroad Hyper 7 and may need to replace the MGM in my onroad Hyper and the MMM is at the top of my list for them both. It's a solid ESC backed up by a solid company that will bend over backwards to help you, failures happen with every company but how you're taken care of after it goes out means everything. I just had a HobbyWing/EZ Run/Turnigy ESC shoot sparks on me and I'm SOL as far as repairs because I bought it in November

When a CC ESC fails I don't really mind because I know I'm covered (even if I have to pay for repairs, it's much cheaper than a new ESC), but with other ESCs you just have to swallow the loss and get a new ESC.