Is this sander worth it over a corded random orbital sander?

If you already own DeWalt 20V MAX batteries and work away from outlets, the cordless freedom is worth it. A corded sander gives unlimited runtime and usually better dust collection for less weight.

How long does the 6.0 Ah battery last?

Runtime depends on speed and pressure, but owners report long sessions on a single charge at moderate speeds. Heavy sanding at full speed drains it faster.

Does it use standard 5-inch sanding discs?

Yes, it takes standard hook-and-loop 5-inch discs, so consumables are easy to find.

Can I use my existing DeWalt 20V MAX batteries?

Yes, it runs on the 20V MAX battery line, including the included 6.0 Ah pack and smaller packs you may already own.

Is it good for sanding drywall or overhead work?

It can handle those tasks, but the weight makes long overhead sessions tiring. A lighter corded or compact sander is easier for extended overhead work.