I have had these fitted permantly for years, even though my Morgan is a 4/4, as it certainly helps on those hot summers days drives to Le Mans.
Like you, I'm oftern told "your bonnets open mate" even from Morgan owners. But I can live with that.
My car came with leather ones. I took them off. The leather was hard and there were minute signs of wear to paint but caught early enough to polish out.
As for the rear corners, I now have extenders to open a gap to let hot air flow out. It's a Plus8 and generates a lot of heat. They seem to be working as fan cut-in has reduced. People do "warn" me about the bonnet being open due to the gap.
