It has been quite a while since Supra III was made so I'd be a little worried about the age of the stuff being sold.
Someone is selling Ilford MGIII as well which is OK as long as the buyers know that it hasn't been made since 1994! It mught be fine as might the MGIII even if at least 16-17 years old but sellers should say what age the paper is and also that it was superceded by Supra Endura.
I haven't looked at the ad so this is not an accusation but too many sellers use the word "new" when they simply mean unopened. In the case of paper new and unopened are NOT interchangeable words.