Well before everyone goes getting their collective panties in a bunch... most of these bottom cleaners use Oxalic acid as the active ingredient for doing the actual cleaning part. This is an all natural, non gmo, free range, 100% organic, fat free, cage free, naturally occurring.... even in whole foods.... compound. Certified gluten free. It is not a harsh synthetic "world as we know it" ending chemical. It's not even outlawed in the people's republic of California.
I prefer myself to buy it in concentrated crystal form, mix with hot water and spray on, let sit, scrub the bad spots, rinse and repeat. Works awesome.
Now clearly it's not a good idea to eat or drink this stuff but nobody is suggesting that.
https://en.wikipedia.org/wiki/Oxalic_acid