To answer your question about the advantages Steve, what it does is spread the sanding motion over a large area, unlike a disc sander that just spins and concentrates the grinding on a small area. DA's are great for final body work where you want to level out a large panel (like a hood). You simply start it and move it over the surface and it sands a little bit off without digging into any one spot. The "dual action" name comes from the fact that they 1) spin in a circle like a regular grinder and 2) travel in and orbital pattern to spread the sanding over a larger area.

We even have a couple of HF ones that aren't too bad, and for the average hobbyist they are fine.

Don