I've used it on a badly rusted Savage No. 4. It was truly amazing. ALL of the rust was gone.
I've also tested it on various other items, such at badly rusted exhaust clamps. they came out looking new.
i'd highly reccomend it.
However, it doesn't last, so get together a few projects to do all at once.
I have one jug left, if you're anywhere near edmonton, I'd be glad to get in on ordring some more, and spilt shipping.