I am using them on steel and I am very happy with how long they are lasting. I have used one stone for more than 3 hours and it is still usable but is getting short. I did have one where the stone spun on the shaft after about 2 hours of use.
They seem to be mounted fairly truly so you do not get much if any wobble.
You can get different finishes by using different liquids such as water, cutting oil, synthetic oil, even rubbing alcohol.
If the rest hold up as well as the first few then I will be ordering them again.
Great product. Works pretty well. Have been using to polishing crowns and composite restoration after finishing. It leaves a smooth surface. The bur is big so you can use it multiple times after sterilizing.