These have worked perfectly for the drill sizes I have used so far. I just make sure to tighten each side about equally, and the fit is very snug. I think they will work as advertised on the sizes for which they are designed. I definitely like the fact that only two stops are needed for multiple sizes of bits. 

They do not have any additional surface coating to protect the wood, so a light sanding would probably be required after use. The only downside I have seen is for short drill bits, the thickness of the stop might not leave enough of the bit exposed behind the stop to clamp securely in the drill. But I think the thickness is one reason they are so secure.