I had no idea they made flap disks with rounded corners now. Just picked up a couple of these to try out and they work great for smoothing out fillet welds—you can get into the corners and smooth the weld down if you are looking for a clean look on table legs, etc. They do a much better job than a right angled die grinder with carbide burr. Only downside is you really need access to both sides of the fillet.
https://www.diablotools.com/products/DCC045040N01F
https://www.diablotools.com/products/DCC045040N01F