here I am again. Well, I was going to order a rust-converter to brush the underbody of my car after taking rust away but......Dinitrol..Waxoyl...Kurust....there is a jungle out there!

What should I get?? I am not asking which is the best, probably they are all ok, but...did someone of you use these products? Which would you suggest? Sorry for bothering for this apparently boring question but all these products are almost unknown here...
thanks, as usual,
Luca