After a while you tire of removing them after use. One - the smaller one - has remained in place now for several months.
The bigger one stays in place for several days at a time....and then falls off. It might take a few goes at getting it back in place (sometimes a gentle pull is enough to dislodge it) but once you're happy with the fit it might stay there for as much as two weeks.
So, if you can't have one screwed on, these are definitely worth it.
But the smaller ones are probably better than bigger.