I've got a couple of Edge XU's that I manage with a single R55 SmartCenter. The current v6 firmware is pretty good. You can go look at the Discussion Boards at
http://www.sofaware.com and see a lot more information.
There's a few quirky things, like the management is by the Backwards Compatability module. When you update the firmware, you first have to update a set of files on the SmartCenter or you may not be able to manage them until you do. You won't make that mistake many times. :-)
There's a local medical insurance company (one of the biggies) that uses dozens and dozens of them for their remote locations.
Ray