JuJu, my husband uses something like that, not because of money but because he has a bad astigmatism so he can't have his prescription lens curved or wrap-around, as most cycling glasses are. He likes them fine, and no, they have never popped out. He said there was an adjustment period, though, and that at first everything looked a little blurry.

That is the big concern with prescription sunglasses, the astigmatism issue. I have a mild astigmatism so I can wear most sunglasses as prescription lenses, but it does take a while for my eyes to adjust to them, too. Unfortunately my astigmatism is getting worse and the doctor said my next pair will probably need to be the insert style.