My HP Envy 27 all-in-one is a few years old now, and this summer it started doing thermal shutdowns daily. I opened it up, carefully cleaned off the old factory grease from the CPU & GPU, and applied this. Haven't had a single thermal shutdown in the months since!
In my computers, Zalman grease seems to last longer and provides greater cooling capability. Other types of grease broke down sooner and required more frequent applications. Syringe is easier to use and doesn't waste grease.