M&M doesn't suck vs toss, only in mid/late game. If u can get 12 marines and 2 medics (some firebats if he makes lots) before he gets reavers or templars it can be very effective. Of course u have to switch to metal right away but u will get an edge if u pull it off.
M&M vs terran sucks tho, 5 vultures or some tanks can kill an army of marines...