That is right they are both Chelating agents. Evapo rust does not tell you what they use but the nose knows.
that once you soak rusty objects in either product the smell is the same. (does not smell like molasses) . You will also get that exact same 'blackening' of the surface. Leave it it wont rust again. Ron, did you not notice the smell on your hands after handling the slimy black part? That is the same smell as you get from a molasses mix or from the product they spray by the tanker load on boiler tubes.
Could be Evapo rust uses something else as a chelating agent but the results you get will be the same. You either use a DOW chemical product (nothing wrong with that as DOW likely grew the cane LOL) or you use a cane sugar by-product. (maybe think of it as ferric nitrate crystals vs. vinegar and steel wool?)
Try mixing a quart of Crosby's Fancy Molasses with equal parts boiling water. Throw in something rusty and check up on it in a week or three. Handy jar to have in the shop. (just keep the yeast out of it LOL)
re harming the part, I have never seen molasses do so. I have left Morse Taper drills and a Morse Taper socket in a bucket for a summer. I just mention that some Australians do claim it can eat parent material and I do know that there is a difference in the bacteria that colonize a chelating slurry depending on temp/environment.
Edit:
just did a google search and the ratio of water to molasses varies by source. Museum in Auckland reports using as little as 10:1 (pale yellow), Chemical hauling ships 6:1, tool restoration in new england 1:1.
I aint inventing any wheels........