I stand by my gains with the MM custom grind but this is one of several good posts I have seen about Inertia. It is good to have choices, few, but better than none.
A bad tuner/tune will also get you no/little gains. There is a guy on YouTube (Chanty I believe) that gained 15 rwhp with one of CompCams standard off the shelf cams. Tuning was done by a local shop. After getting several recommendations he went with a well known tuner and last I saw was at a 45 rwhp gain for the cam install.