My glasses are small and oval-shaped and these clip-ons fit fine, fully covering the glasses.  The spring mechanism appears sturdy and well-made; the actual lens feel a bit flimsy so I try to make sure they're in a case of some sort anytime I'm not using them. I don't think they'd fare well thrown in a pocket or the bottom of a purse unprotected, say.  It's helpful to take out a ruler and look at the metric measurements on it in order to gauge whether these clip-ons will fit before buying. After reading the other reviews, I made sure to do that.  Good little product.