But he doesn't show how his coatings stand up to an angle-grinder
Yeah, that is a pretty good demonstration.
I heard of a coating lifting off (literally floating off) a mirror when the mirror was placed into a tub of warm soapy water! It belonged to a junior member of the BAS 20 years ago.
He wasn't taught how to clean his mirror so he decided to wash it himself without asking how.
He said he filled a plastic tub with warm soapy water, slowly dropped the mirror into it face up, and with horror watched the aluminium lift off like millions of tiny snowflakes!
I'm glad they don't coat mirrors like that any more.