I have used two over the years. The first one was a simple homemade model- 100 mph tape and some foam padding. Cut it to fit me- if it wears out just replace the foam. Worked very well. I now use the Blackhawk cheekpiece, the model with three inserts. Use the appropriate inserts so you can get the eye relief, you can take it off and still have the same fit.
If you do get a stock with one, make sure you know the height, say if you clean, move it down, then you will know where it goes when you move it back.