There is definitely a huge difference in cutting ability & lifespan between brands of cutting discs, grinding discs , flap wheels, etc. The better ones from a supplier might even be much cheaper than from the home stores.
For cutting discs, I prefer the quickie thin discs & usually use a 6" in a 4 1/2" grinder. This is NOT something someone without an excellent feel for a cutting tool should do as it is dangerous without proper precautions. The 6" diablo blades from home depot are about the best a homestore has to offer. A cgw stainless quickie disc is one of the best I've ever tried & has outlasted others about 3 to 1. Many of cgw's flap disc wheels are pretty good also, but I haven't used enough to have a favorite .I usually buy the coarsest flap discs [40] since you're into worn paper pretty quickly.
For a final grinding/sanding on metal, sometimes I use what they call a milk wheel.
I did get to try out someone's professional mini belt sander before. It is a pretty cool tool where you have an appropriate need for it, but aren't all tools? Someday I'll have one. Part of it's advantage is reduced heat from lower cutting speed.
Since the economy dropped, I have occasionally found nice tools for cheap between the junk a pawn shops, but it takes patience & luck.