I have in my shower provided two existing wall plugs with two hook bolts and the shelf securely suspended therefrom. The vacuum cleaner I have fixed right and left on the shelf linkage so that they prevent slipping.
When hanging the loaded rack over shower or bath using the two suction cups must be accepted that a crash damage to the enamel tubs.
As I have described the shelf mounted after I have made a few changes to it.
I renounce reason to return, but no one would necessarily recommend.
Also, the price is relatively high compared to other shelves.
I regret to write anything more positive.