Review (4/5): Pleased.
I was concerned that these would have sharp teeth that could potentially damage my hair. But once they arrived, I saw that the teeth were slightly rounded at the top and smooth to the touch.
I was also concerned that because of the cheap price, the metal spring might rust. But after owning and using these for several months, I've seen no sign of that.
I like that they grip my hair firmly, but not too tightly.
The only thing I don't like is something a few other reviewers mentioned. The top part of the clamps that you squeeze together has sharp, pointy edges. So, one just needs to be careful when using them (or file the edges down with a nail file).