Mercasol Vs Dinitrol Vs Buzzweld

[ADP68]

Hi, I am buying a Classic Range Rover which is solid underneath but has v light surface rust in places which I don't want to worsen. I was wondering what people's experiences of having their cars professionally treated with the aforementioned products.
Mercasol - not heard of it before and costs about £550 including cavity injection
Buzzweld- about £950
Dinitrol - about £620

Does anyone have any opinions please? I am based in South Bucks and can't do this myself. Thank you