I've been running Revo for about 9 months now. Not a single hiccup. I ran Revo on my S3 for 2 years (Stage 2) and not a single hiccup or issue.
I'm not surprised Revo puts out more than MTM. One is a proper flash, the other is a piggyback box. I ran a DTUK on my S3 before switching to Revo. Night and day difference. I'll never use a tuning box again, unless there are no other options.
MTM warranty...if it's anything like the ABT warranty, you'll need to prove without a doubt that it was the ABT box that caused the problem. The onus will be on you to prove it as well. I know two people first hand who went through hell with their ABT warranty claims. In the end they gave up, as it would have required legal representation, and the costs outweighed fixing the car themselves. So be weary of any promised warranty from these companies.