I own the MT-2 personally, and I'd rate it as a moderate, just "okay" pedal. It has a HUGE range of adjustment capabilities, and I have a feeling that most people that say it's crap just haven't played with their knobs enough (lol double entendre). They're EXTREMELY sensitive, and the tiniest adjustment changes your sound dramatically. You can pretty much get any sound you want out of it.

However, no matter what combination you arrive at, the biggest problem with the pedal is that it will always sound very digital and artificial. A summary:
Pros: huge range of adjustment possibilities
Cons: always will sound hollow and artificial

The Electro-Harmonix Metal Muff, on the other hand, has a lot more realism and beef to it. On the other hand, I don't believe you can adjust it as much, but I don't think you need to, as it sounds pretty much amazing however you set it, unlike the MT-2, which has a lot of horrible, horrible possible configurations. However, I've never actually played one, I'm just going by the youtube demos I've heard. For comparison, here they are (none of these are me playing btw):


Metal Muff:
http://www.youtube.com/watch?v=MCrFvrpy6Zc (not in English, but still you can hear the sound of the pedal)
http://www.youtube.com/watch?v=BzfStJAU73Y (not the best playing, but good sound)

Listen to all of those, it'll take you 5 minutes, and then decide which you like best.
Squier Strat
B-52 AT-212 100w tube
Boss Metal Zone

Amateur philosopher and physicist