I have had some of this is the garage for a while and never really got round to using it. However, I recently had to clean up the steel wheel hubs on my car trailer ready for new tyres, and the inner of a couple were really rusty. After wire brushing the majority of rust off, I painted the hubs with this rust cure and have been pleasantly surprised by the results. It's a sort of thin white cream prior to application, then after a few minutes drying any remaining rust goes black, and the surface is also waterproofed. The wheels look very good, and it can be primed and overpainted if necessary.
I only have a small pot of the stuff, and it was £7.50 or something, but a little really does go a long way. I'm impressed.