If you don't use raidz(#), then freenas isn't for you. Period.
Certainly FreeNAS is appropriate for using mirrors, which aren't classified as RAIDZn. I can even imagine use cases where other characteristics of ZFS (snapshots, for example) are more important than data integrity, where you wouldn't want or need redundancy (though I expect those use cases would be rare). In such a case, FreeNAS may still be appropriate.
@duttytd, people here (including me) are going to assume that you care about your data and want to store it in a secure, redundant manner. That really requires, for any OS, using server-grade hardware and ECC RAM, and really using a next-generation filesystem like ZFS or btrfs. This need not be terribly expensive--you can buy a prebuilt server that's suitable for under $300US, not including drives. ECC is somewhat more important for ZFS than for some other filesystems due to the way it scrubs your volume to ensure consistency, but a RAM error with any filesystem will hose your data. This also means using some sort of RAID arrangement for your volumes, whether a simple two-disk mirror or something more advanced.
If those are not your goals, you're better off looking at a different NAS OS. You may be able to do what you want in FreeNAS, but you'll be fighting the design of the system. There are lots of free NAS OSs available, and FreeNAS isn't for everyone.