Teflon coated STI mags.....
I have never tried them either, and all of my STI 2011 mags in various lengths work fine.....
I would presume a teflon coated mag would be super slick on the inside to help reduce any friction when the rounds move up the tube, but I have never had any issues with my standard STi 2011 mags, after I tweaked/tuned them....