TF-4 fixer is a product of Photographer's Formulary, and is as far as I know a proprietary formula. I use TF-4 for all fixing tasks, i.e. film, RC paper, and fiber paper. I think it's a great product, and have thus far seen no downside to it. It's particularly helpful in printing with fiber paper. As to "non-staining": from what I've read, selunium stains occurs as a reaction to residual acidity in paper from typical rapid fixers. I used to get stains; now I don't.
Formulary is located in Montana, seems to be a small company, and is dedicated to B&W photography. I also use their 130 paper developer. It's great stuff, and the working solution lasts for months. I'm also experimenting with their WD2D+ pyro/metol film developer. In fact, as we say in the South, I'm fixin' to whip up some WD2D+ here in a few minutes.
Anyway, I like to support Formulary to the extent that my meager photo budget permits, as I do with Ilford and some of the other few companies that are committed to traditional B&W.