I am not an expert on this but I believe XFS has performance advantages over EXT3 however the downside is that I have not found a free Windows utility to read the XFS disk via windows (other than through the NAS). This was the reason I stuck with EXT3.
Google EXT3 vs XFS and you will see a ton of debate.
I believe that the utility will allow you to read or write. But remember that the utility is only needed if something goes wrong with the NAS and you can no longer read or write through the NAS.