I've used a non-Festool, certified HEPA shop vac. I'm not impressed. You have to use an overly-expensive (certified) bag that has a flap of tape to close the opening when you remove it from the vac, and a paper cover (looks like it would leak where the retainer ring causes it to wrinkle at the top) over the main filter. Other than that, it's a regular shop vac. I have a regular Shop Vac brand (the standard large one), and when I put in a HEPA filter (I don't see how dust could get around this thing--it's rubber gasketed at both ends and the retainer keeps it tight) and a drywall dust bag inside (also has a rubber gasket in the opening that fits snugly around the deflector just inside the hose opening), I can use an ROS to sand drywall without a mask and the air will be CLEAN. I did it once over hardwood flooring, and there was nothing on the floor when I was done, not even the ultra-fine dust.
If you can afford a Festool vac, knock yourself out. I probably could, but I don't see the need. I'd rather have a vac that I can abuse a bit more, and if I kill it, I'm only out $100, not $600. And, I've killed a few--but in almost 17 years, I still haven't spent $600. I also don't think it's that loud.