Well, it did get hot on the back. Whether it is uncomfortable for you or not depends; since I was a waiter in college, my hands can hold flaming hot plates while aunt Mildred puts her 2-ton purse away for me to set it down...
So, I did 2 panels that night, but only recorded that one (it's enough!) so that's 2 hours with the RAS-115 and RO-90 non-stop. At the end, I was getting tired of holding them, for sure, but I never had that numbing sensation you get from bad sanders. I'm hyper-sensitive to that due to carpal-tunnel problems.
One thing that may not be noticed as much is the amount of dust. Even though I'm using the sander on edge where its DC holes are at a disadvantage, I had very little dust when I was all done; chips, but no real dust. Let's just say nothing settled into my stein to make its contents taste like Mahogany Ale [embarassed]
If you're curious, the panel at the end isn't done. I left the embossing proud because of what I want to record for the podcast; it'll get dropped considerably with the RAS-115 then finish-sanded with the RO-90 using 2 different interface pads. Normally "grinder sculpting" is a disaster of dust and chips followed by boredom with hand-sanding. I wanted to do this to see how it works to eliminate that part.
-- Speedy "¡Ándale! ¡Ándale! ¡Arriba! ¡Arriba! ¡Hepa¡ ¡Hepa! ¡Hepa! Yeehaw!"