Haven’t used Metal Rescue but I tried Evapo-Rust on my last project, a 750 tank with mild rust. I’ll never use anything else again. That stuff worked great and was soooo much less hassle compared to the other methods (electrolysis, toilet bowl cleaner, muriatic acid, citric acid, other ineffective stuff).
If the Metal Rescue products is the same concept, I think you’ll be pleased.