It's not good for high heat. I've seen it harden and flake off.......even in non heat applications. It's just personal preference, I don't like the stuff. lol
In the oil patch especially, we installed a lot of fittings for stainless tubing. We used the thicker teflon tape with two wraps. Then just a dab of PST paste. Rarely had leaks even in 5,000 PSI installations.