I haven't used Metal Rescue, but from the looks of things it's just calcium bicarb (Ca(HCO3)2). If you're patient, you can probably get equally good results with a molasses soak.

There are lots of chemical rust removers that work. The issue is that you have to be able to submerge the rusted area (often difficult on something large and unwieldy like a bicycle frame) and in many cases you have to neutralize/remove the chemical afterword (which can be tough for places like inside the frame tubing). Also note that you usually have to strip the part down to bare (rusted) steel. That's usually more work than the rust removal, and in some cases (media blasting) takes care of the rust for you. Also note that deeply rusted areas may need multiple treatments with manual removal of scale in between to expose the deeper oxide. Lastly, some chemicals will etch the metal in the process of removing the rust. That may or may not be a problem depending on the application.