Personally I don't think the grip on the fly rod will either make you a better caster or poorer caster. What I do think will improve your casting is lessons from a certified instructor and practice. In reading/listening/ watching great casters such as Lefty Kreh and Joan Wulff, I have never heard them suggest or imply that you needed a customized grip to improve your casting. The only time I could see a specialized grip helping is if you hand had a physical deformaty of some kind, or if you had unusually large or small hands.

But the article is interesting.