And more importantly needs to interface properly to the nas os...or it's just going to delay shutting off without a warning.A UPS for a nas doesn’t need to be huge, unless the nas is huge. It needs to keep the device running for 5-8 minutes to allow the device to shut down.
This being said though, I've run most of my units without a UPS and they're fine after a power outage even without a shutdown. Still a good idea to shut it down and reboot it if you did have a power outage without a chance for it to shutdown properly.