There is a lot of mention of price here. I don't think anybody has mentioned this angle.
If your a first time buyer who is considering the other style bag of a decent quality lets say it will cost you about $100.00 (yes I know there are good bags out there for cheaper, but work with me here) you also then have to buy straps. Straps are around $50.00 for high end pair. So your up to $150.00 for the other style bag with new straps.
The grip bag is $200.00, $50 difference does not seem like to much.
Having said all that I still think the grip bag and some others for that matter are over priced. But we keep buying them so,,,,,,,,