I did consider a NAS a few months back but they seem very poor value for money, the good one's are expensive as half a dozen hard drives, and even the bad one's are pricey. I ended up just shoving a few new drives in my PC case and using them locally to my PC. I cannot think of much of a disadvantage to what I am doing vs buying a NAS, other than a bit more flexibility with the raid setup. Now of course if I didnt own a PC which has 9 drive bays in the case, the story might be different, e.g. if I only had portable devices.
If you can get a FREENAS compatible unit then thats a good choice, as ZFS is the best filesystem out there in my opinion if you want data resiliency.