Supposed to be pretty effective. I saw someone post some blood-work while on a cycle of methyl-d and M1T, and it looked to be working pretty well.
I don't think it's much of a bulking substance, rather for cutting or the like. I think it hardens more than it builds
Some people talk shit about stacking it with M1T because of liver toxicity, but I don't buy into it, as long as you don't over-do it with the M1T or the methyl-d.
Some people get good results with just 3mg/d, others go as high as 10. But I, personally, wouldn't go over 5.