Specs?
Price?
Warranty?
Web site?
From what I've read in the Slim Devices forums, particularly from European customers, energy use seems to be one of the biggest concerns. Heat output and the need for fans, and therefore noise, are closely related. Unfortunately, performance is inversely related and SqueezeCenter can suffer badly on underpeforming hardware.
What kind of user interface is used when ripping CDs? Can it be done headless or does it require a keyboard, monitor and mouse? If it's intended primarily as a headless server, then there's not much need for CD ripping, since the majority of users will have other PCs on the network. If it requires a keyboard, mouse and monitor, then that may be a deal breaker for someone who wants to just park the thing in a corner.
Warranty and support will be key, but realize that you'll be selling these primarily to the not-too-computer literate, so any trouble with SqueezeCenter will come back to you as a support incident. That could be a nightmare, or could cut drammatically into margins. I've been using SlimServer/SqueezeCenter for about four years, and frankly, it's not something I'd want to support.
Oh, and if you call it an 'NAS' you'll sell 10x the number. Those not-too-computer literate folks mentioned above have strange ideas about what is a computer and what isn't. If you don't attach a monitor, add some sort of of RAID implementation and call it an NAS, they eat it up.