If you have a vertical drill press, this is a great set of diamond hole saws. Works great for cutting out the holes for pipes in marble tile, slate, etc. Comes in a nice little case to keep everything organized.
If you are trying to use these with a regular hand drill, it isn't easy. Unlike wood hole saws, there is no pilot bit to stabilize and center your hole. Since there is no pilot bit, there is nothing to hold the saw against slippery marble or ceramic tile. If you just try to go at it, the saw will walk right across the front of your work and ruin it with huge scratches. To avoid this, you have to VERY CAREFULLY AND SLOWLY seat the saw edge into the hole by running the drill super-slowly. It is hard to tell when you reach the point where you can turn up the drill and just power through.
Definitely practice on some scrap pieces before you try doing this with actual work you want to keep. You can get the hang of it eventually, but it takes a little time to master the technique reliably.
Once seated, they cut through even thick stone with no issues and they don't seem to overheat quickly. They seem reasonably durable, and with light use they should last quite a while.