+1 I will Be using their range of products later this year to treat the D40. All their products (according to various reviews) are top notch . S50 is usually used for inside the chassis, Dynax is tougher for external chassis & whole body ( 2 coats ). There is a clear ( yes clear ) dynax for visible areas.
They do a range of rust killers/converters & pre-paint preparations They show comparison tests for the rust products, to show their products perform against the competition.
I'm looking at making a rust killing home brew, using citric acid & a paste.
This vid begins with a brief history of the firm
https://youtu.be/4M0y7IWIZAc before reviewing their detailing range. Worth watching the whole thing.