For cutting naturally, I think it is legit. I had a long natural stint (7+ years) between my roid periods and I will tell you that glutamine and HMB before cardio allowed me to maintain my strength and size while shedding 15-20 lbs of fat. Believe it or not! If you are coming off cycle from roids don't expect HMB to make you keep all of your gains from the roids. Going from 500+ milligrams of Test (or whatever stack you like) per week to natural or suppressed levels will result in some loss of gains, whether you take HMB or not. But if you are natural, MRPs and creatine and glutamine and HMB do, in fact, help your efforts.