They slide off and if you don't JAM them on, you might lose some stitches. I think I prefer the singular point protectors. But since I have these, I'll keep using them, with caution.
These protectors stay on your needles. They do fit needles from size 1 to 10. Very handy and I'm glad that I got them. I don't own any size 0 needles so I don't know if they fit size 0.