I think Meguiars and 3M also do some kits. The TW video makes it look quite easy Turtle Wax Headight Lens Restorer - YouTube. I just use some wet and dry paper and finish with a polish but the process is very similar
No, all you are doing is removing a thin layer of the plastic lens to get down to the clear stuff so it can come back. Worth using some type of UV protection on the lens to slow it down, sealant or even wax will probably help.
Probably would help if done right, would try a google off it for the right stuff to use though, or possibly a clear film with some kind of UV protection in it would do the same job and stop any stone damage at the same time.
I used the Holts kit but finished them off with the Meguiars kit. Holts kit gives you a small disk to fit on an electric drill and various grades of wet and dry which you need to use until all marks and scratches are taken out then use the polishing sponge disk. I found the Meguiars kit with just the polishing compound and the polishing disk they provided produced a better final finish but it is no good for any deep scratches or marks. Once polished you need to seal lens otherwise it will happen again.