I found an interesting forum thread over at the avsforum discussing the advantages/disadvantages of Flexraid vs Unraid and Snapraid for use as a NAS. The thread starts out with a quote from another forum detailing some of the features of Flexraid:
1. FlexRAID works with Windows (WHS, Win7, etc). It's a driver on top of Windows.
2. Can start with full disks! I know unRAID needs empty disks.
3. Multiple parity drives, to help recover from multiple drive failures.
4. Works with any disks on your machine, even directories (parts of disks) and networks shares. Meaning, you can create parity to protect physical drives on your media server, as well as other drives on other machines, like that USB drive you have connected to your router.
The second post in the thread chips in about Flexraid's advantage of using a standard window's file system:
I use Flexraid on a normal Windows 7 install. Works great. The other advantage is that if you lose one more than your number of parity drives, you only lose the data on those drives. The drives are all just in NTFS format, so they're readable from other computers.
I haven't heard of any major bugs or people having corruption, although raid/uRaid/Flexraid/etc. are no substitutes for a true off-site backup solution.
The thread goes on for nine pages (as of this writing) and has a lively discussion of the pros and cons of various parity and drive pooling solutions. Recommended read!