Is Kodak Flexicolor SM (C-41SM) Tank Final Rinse a good stabilizer?

It will work just fine! Initially, C-41 film stabilizer was a surfactant (FhotoFlow) plus formaldehyde. The formaldehyde acted as a biocide to preserve the film from attracks by mold and other beasties. Secondly, the formaldehyde formed a peptide bond. Film uses a binder of gelatin to glue the light sensitive goodies and the dyes to the film base. Gelatin is an organic, made from animal bones and connective tissue. As such it is food for bacterium. The dyes are also organic, they are oily globules. Under the microscope, gelatin resembles spaghetti. The peptide tacks the spaghetti stands together at places where they overlap. This restrains the dyes preventing them from being mobile. As time passed, the formaldehyde was labeled a carcinogen. Color films were modified so that only a biocide plus surfactant did this trick. A modern C-41 rinse does this deed; it contains the surfactant plus a mild biocide similar to that found in antibiotic hand soap.