My little jar of Naval Jelly says that it contains phosphoric acid and that it should NOT be used on aluminum or chrome. Works great on iron or steel.

I don't know what it does to paint… suppose it might depend on the paint. Just ran a little experiment on the corner of a toolbox and the surface looks fine but a little bit of color did transfer to the rag. I'd guess its not going to strip the paint but won't be great for the finish. YMMV.