What is HMB going to do that a full protein and/or BCAA mix wouldnt accomplish? Save your money.
That is like asking "what is leucine going to do that whey protein won't". The amount of leucine that metabolizes to HMB is very low (about 5%), so you would need to take a very large amount. Also, there could be effects that are only noticeable in its free form.
There seems to be conflicting info on HMB based on published research. This could be due to many factors from how carefully the study was designed to the timing of supplementation.
I'm interested in HMB due to its possible effect on mTOR. My hope is that it will work synergistically with leucine. I just ordered some and plan on dosing 2g along with 5g of leucine with each of my backload meals.