I do well over 200 euro's a year for customers. Personally, I do not recommend any hard cleaners on a skull. I use dermestid beetles and maceration as my cleaning processes. Once the skull is clean, I alternate back and forth between dawn/heated water and 50% peroxide. Once all of the grease/fat is out, you will be able to tell when that happens, I use another process for the final whitening.
Lone Star Skull Works
Texas European Mounts