I purchased these clamp on lights hoping I could use them at the top of my easel, to shine down on my painting but they won't swivel back towards the clamp. So, for me, for the intended purpose, they are useless. e.g. if you clamp at the top of a book case the light can't be swiveled back toward the bookcase to shine light in it.
For other purposes, the clamps is very strong and opens quite wide. The part that does swivel is not smooth and I'm not sure about how it would wear. Of course, the metal shade gets very hot and you have to be very careful. The cord is short and to use it above waist high you'll need an extension cord.