I've read in various places on the internet that JP Weigle's Frame Saver will stop existing rust.

This is something I'd like to believe, however, it doesn't really make sense and my common sense tells me it's not true. I don't see a JP Weigle web page- so I don't see anything official from the company- just people talking.

I recently bought a bike that looks quite pretty on the outside, but has some rust issues in the seat tube- I assume it's in the other tubes as well.

So is this truth or fiction?