You could just build yourself a cheap PC and maybe get a lot more use out of it (say plex box) down the road. The cheap QNAPs are ok I had one for a little while and even ran Twonky for a media server. I ended up just using an old gaming laptop now for all that. I also use dual backup drives on seperate PCs over the network for important files in the event things go tits up. Mirroring software is free and abundant. You could also do a cloud solution depending on what you're backing up.
With 2 bay NAS you'll have the option to mirror the drives or use them together for more storage IIRC. it's been a long time.
Really though, just get yourself a cheap laptop or build a cheap pc and get a ton more use out of the box.