Mine arrived a few days ago and, as long as you dial the correct wire size on the adjusting wheel, they work great for teflon, PVC and silicone insulated wire. In fact, just last night I used them to scrape off the lacquer coating on magnet wire, (make several passes with that stuff).
Ed, indeed it was teflon. Drove me nuts as fingernail, Xacto blade, etc. seemed not to work for me. Thanks for the tip, I just ordered that special stripper, so I’ll be ready next time. Take, that, teflon!