I never said there was no difference, just that I couldn't hear one, in my system, or with the five different 301s and 401s that were tried. The only reason to change the idler wheel is if the rubber has perished, or the bushings are worn. Clearly the idlers of the Garrards I tested the AS with were in good condition, and they were. I have replaced many idlers, but I couldn't discern a difference between a good condition standard idler, or the AS. Doesn't mean there isn't one, but maybe I'm not sensitive to the type of change it produces. Who knows, or cares!
I don't claim to be any sort of golden-eared guru with magical senses of perception, but I do have my own experience to draw from. YMMV.