There is more to a hole saw than just speed in cutting. They have to be able to last a long time. The material must be able to be removed from the hole saw easily. Also, the line of sight has to be good so you can see where you are cutting. Blu-Mol Xtreme hole saws hit each one of these points and were very impressive to use. There is a presence of quality when you pick up these hole saws. The M42 Cobalt construction and thick back stand out.