We have plenty of customers using GlassCast 3 on worktops with no problems. In terms of temperature experience, we have tested quite a few resins over the years and not found any that offer any real high temperature benefits over and above other resins. With heat resistance, I would always be wary and see if you can find some independent or customer reviews on the long term resistance. There can be a difference between briefly placing a hot pan on a surface and leaving it there to cool down. Also time and if physically possible, a elevated temperature post cure will all help improve heat resistance to be the best they can be.
It would be something that would be ideal if all the resins on the market could be tested side by side to see which ones perform as advertised or better.
However, to be on the safe side, we would always recommend using a placemat or trivet to prevent heat damage on all the resins we have seen, including GlassCast 3.
Easy Composites / Carbon Mods - Technical Support Assistant