I haven't seen any of the videos but one that I found on the web. The thing here is that you will see a lot of nice info of the basic sort with the guy moving the glass about but a lot of the stuff that deals with the grinding is still missing. From reviews tho, all of the commercial videos that I've heard about do a decent job of showing how to do the grinding and polishing.
If you feel the need, go buy one and watch it and report after you have ground a mirror on how accurate the video is to your expectations.