I haven't tried them for lifting, but I think Montague is right about it's density.
I don't think I will become a fan of thick grips since my grip strength is already the weakest point when I perform deads/chins/rows/etc. As a result you can't train your back to the max. I would rather suggest DB wrist curls with palms facing up (flexors) & the same with palms down (extensors).
Exactly. I liken it to performing db presses on a Swiss ball. You're sacraficing working your chest because you're simultaneously working your "core" by balancing your ass on a beach ball.
If you want to train chest, train chest; if you want to train abs/core/chain, etc., then do that. Doing both is not always the best idea.
Likewise, why cheat your back just to work your grip more? Some trainers may like that idea, but I'd rather separate the two.
See our latest Forearm thread on the Training board.