The only time I've felt anything get hot was an old plane blade that was very banged up. I was hogging off a lot of material for a while. Even then, it only got warm, not too hot.
In general the heat sink seems to work pretty well. That, coupled with the fact that you are only spending a minute or so at each grit setting, seems to keep the blades cool.
I likey mine big time!
Now I don't have to work with dull tools (or buy a new one every time I need something sharp

).
J