Yes, big difference with the custom tune. The email custom tune process with HemiFever goes like this ...
You install the DiabloSport canned tune and modification parameters you want.
You email HemiFever a copy of your stock tune file and the canned tune file ... along with the answers to their questions.
HemiFever emails you the custom tune. After you install the custom tune you email HemiFever the data logs they requested (data logs collected from the DiabloSport programmer).
Based on the data logs, HemiFever emails you a custom tune update.
So instead of a one-size-fits-all tune, you actually get a tune adjusted to your engine.