I have used the sandpaper dots you buy for the ruler. I've not had any problems with wobble. But, I then to place things evenly along the ruler. To me they interfere with seeing the lines. I prefer the plastic that is called "Invisi- grip". It works by static cling. It helps a good bit. I still use a suction cup handle that I bought at the quilt shop.
I'll have to make a trip to Walmart for the bath aid. I find the handle on the one from the quilt shop tends to come off the suction cups and it's not very ergonomic. I have trouble with both my hands from arthritis and from surgery to remove some tumors. The larger handle of the bath gripper would work a lot better. I have one of those in the bath.