Well, I do know a few things about them. I believe they were the best penetrating head from Dr. Ashby's reports. They have a single sided blade which is suppose to be the sharpest out there. However, it is also one of the hardest to sharpen, and I no longer use them because of it. Others I know have also given up on sharpening them. But, there are also people who are experts in sharpening them.