I looked at the Sew Slip, & although they do not say for sure, I believe this is a teflon sheet as well, with the silicon backing for cling or tackiness. (They say it is heat resistant up to 500 deg., it is stain resistant, fabric thin, etc., and from the pics it looks like teflon.) All that said, if it really is teflon, you will be able to use it for years to come, making it a worthwhile investment.
The Free-Motion Slider & Supreme Slider is basicly the exact same product, and they actually tell you it is teflon. Look at this link and you can see the similarities between the 2 products: http://freemotionslider.com/