Hi Dave;
These are your best friends when making welds look good. And they don't just make them look good. Sometimes a bad looking weld still has sufficient strength, sometimes not. Clean it up some and it becomes apparent if it needs a little more and it's easier to lay a little more material down after these clean it up. Also for aluminum it's imperative to start with a clean surface, so these can clean it up quick and easy without removing more material than you want to. But they can remove a lot of materiel, fast if desired.
These are far better than a regular sanding disc. Aluminum can't be ground with a grinding disc as the aluminum will plug the surface of the grinding material and can cause it to break apart catastrophically. As these wear they expose new material so aluminum plugging is not an issue. They do make them in different flavors suitable for different uses and materials, but the standard one works just fine for all.
Todd... making bad welds look good since I found these!