1) Talk to the Customer Service departments of these companies.
2) Choose the one that seems best and order it from Amazon so you can return it if it doesn't seem to grip well.
3) The biggest problem with mounting a rail on a wall is not drilling through the tile, but mounting it securely on the wallboard underneath. Unless blocking was previously installed, it is rarely possible to find a pair of studs that match the rail length. Molly bolts (not plastic anchors) are another option for rail mounting.

For all of the above reasons I was hoping to go with the tub mount, and yes, Amazon has a better price on all of them. I was hoping that someone had personal experience with one of them and could point me in the right direction. If not, I'll have to order and return the item if it does not work.