[Canadiain]

Is this "sanding block" like what you use for autobody work or drywall work, a rectangular piece of material you wrap sandpaper around and which serves as a backup to it, so you get a flat surface?

Similar but not quite, without giving too much away there is a standoff on the block to allow the SiC paper to be used "Against The Grain" without inflicting unwanted damage.

I agree with others that the value of ATG is primarily in the simple clear instructions that actually get you to the end point of a good reed nearly every time, rather than the actual hardware. Mostly since I have switched to Rigotti Golds I only use it for a little side to side balancing rather than any major fixing. I have no regrets at all about buying the ATG many years ago from someone here for about half its retail cost. Money well spent and returned many times over through the number of reeds that knowledge has made playable for me.
If you are old school and have learned to work reeds with reed rushes, razor blades or penknives over the years there is probably little to be gained by investing in anything new.