I think RAID 5 is well over the top for most home users, in fact it cold be argued RAID 1 is slightly over the top as well.
As long as all your important files are backed up in other places (CD, DVD, other external drives or even other computers) then having raid switched off on a home NAS is fine. That way you get twice the storage capacity in the NAS.
Note that most NAS boxes use Linux for running the internal hardware in the NAS box and the hard drives will be formatted in a Linux format, so cannot be read directly by Windows (out of the box I mean). If the NAS box fails and you have to take the hard disks out you need Linux to read them. Not a big deal, but be aware of it.