Pros: Inexpensive, quiet, uses little power. Easy to reset after power outage, easy to install drives. Allows several RAID configurations. Windows network recognizes it easily. For more shared storage, attach a USB hard drive.
Cons: Slow as molasses in winter. Click a file & copy to the clipboard takes a minute! Can't keep the drives from sleeping. And it prevents files from setting the archive bit, so you can't do differential or incremental backups - allows full backups only.