Was just reading about cleaning stainless steel over at trailersailors.com. Oxalic acid apparently works, and strips off any iron oxide so that the chromium can create the barrier oxidation layer. Bartenders Friend is oxalic based, so maybe these other products are oxalic based. It's probably cheaper to buy a tub of oxalic acid at the Ace hardware store than to buy Bartender's Friend, and the straight acid can be used to clean the waterline and bleach dark water marks out of wood.
Brian
Please do not use an acid other than Nitric, which you can't really get your hands on, and citric acid, which you can get. There are only two acids allowed by ASTM standards which are suitable for passivating stainless steel, nitric acid and citric acid. Other acids can damge the metal. Oxalic, phosphoric etc. can damage SS but not passivate it.. It leaves the SS worse off then if you did nothing, except that temporarily the rust will be gone. Yes the rust spots often will disappear but they will return faster because you have not passivated the SS and may have even changed the surface by removing certain materials easily attacked by the wrong acids..
Products like Spotless Stainless actually passivate the SS so rust stays away longer. It also does not dull the finish and is actually good for it, not bad for it... The more you use Spotless Stainless the less and less the rust comes back. I have been using it since it first came out and am a HUGE fan. It is worth every penny I pay for it.....
Spotless Stainless is a very, very concentrated citric acid mixed with some other proprietary ingredients. You can likely achieve some results with store bought citric but just not as fast etc... I actually used to soak stuff in Tang, and it worked okay, and was pretty cheap, but Spotless Stainless works better.