I actually tried m-stack about a year ago. Don't expect any miracles. It's a 21 day "cycle." I gained 1-2 lbs of lbm and a little bit of strength. Probably a result of good diet, training, and sleep. There is one magical pill in the stack that will give u an "animal" feeling in the gym. The first 4 days i didn't get one ounce of sleep. Turns out this pill is equal to about a million cups of coffee. It's the pill that gives the stack a "working" feeling. I removed the pill and the energy level went down.. but my sleep returned. I ended up having 15+ of the pills left over which I just gave to a friend who's training for a marathon.
It's not a total waste of money if you want to remain natural. Has a lot of good stuff in it at minimal quantities.. making it a well rounded supplement.