I've got them on my daughter's CZ. Running a Leupold 4x Rimfire scope, I couldn't use a BC flip-up without the bolt hitting it. Luckily, I found an Alumina flip-up in the Bargain Cave at the local Cabela's for less than the price of a BC. They're really nice rings.
They're kind of hard to see in this picture, but here they are.