Yes, I had seen the double-sided suction cup on here before and had high hopes for it until I read a couple of reviews that basically trashed it (link). It's been discontinued and that could be why. I don't know whether the problems they encountered would apply to all suctions cups or just this product. It's puzzlingly difficult to find a double-sided suction cup big enough for the task (I've tried multiple times).

I hadn't really thought of using duct tape but it might be worth a try. I plan on using it on a tile surface in the tub so I'm not sure how well it would stick. The balls would provide plenty of surface below the shaft on which to wrap tape but there's not much room above. Using some type of O-ring contraption might provide a way to use tape on all sides. It still seems like a PITA and potentially messy.

I guess I'm just disappointed in the fact that there are only 4 VixSkin models with a suction cup. I'm completely spoiled after trying VixSkin and I'm surprised that there's not enough demand for this to compel them to offer more products with this option.