Never used the product in question but there are several rust inhibitors in the automotive market that work exceptionally well and if applied properly would probably add a few decades to the life of a "mildly" rusty frame. POR-15 is one of the best, it won't hold up to UV so if exposed to UV it must be painted over but inside a bike frame it would be fine. I live in the Rust Belt and it works very well here but, as stated above, "Rust never sleeps". Just a guess but Frame Saver is probably very similar, what do you have to lose?