My experience only here. Flitz can be used, as others have stated, with a light touch and IMHO will not damage blued finish if used that way. I also use Ren Wax and Johnson's Paste Wax. Those products are totally non abrasive and serve to protect the finish, but are not effective in removing mild surface corrosion/rust. I buy a fair number of used firearms and Flitz is the first product, then wax. In some cases, a wipe down with oil and a microfiber cloth will remove surface grunge from years of benign neglect.
Much depends on the degree of previous maintenance or lack thereof. Use common sense, start light, and don't overdo.
Any of the mild abrasives such as Flitz, Simichrome, or Mother's Mag and Aluminum polish will change the matte finish of some stainless steel to a high polish if used with vigor.