Jigs make life easier. That is a good one. I could see a good use for that type of jig on my Ridgid ocillating edge sander.
I'm not a fan of that type of disk sander. It may be user error but for me it seems to burn as much as it sands. 
I use a similar jig to cut circles on my band saw. With a sharp blade I can sand the cut smooth by hand.