Hi, i purchased a set of these the other week for drilling porcelain tiles (also 12mm) and they drilled through like a hot knife through butter. This has been one of the best tool buys i have made, because in the past i have tried other drill bits/cutters with not alot of success. I have just purchased the 120mm cutter also, but not had a chance to use yet - but will let you know the result when i have done so. If you aint got a set of these in your kit then i would say it's a must get.
