The firewire will output to a NLE system the same way you can record externally onto a Firestore or similar device, but you cannot input back into the camera thru it. Sorry, I can't speak to any comparison to the XDCAM f350.
It's served me well to be able to record simultaneously to tape and Firestore when I choose to, or just to either individually, as the 900 record button will trigger the Firestore even with no tape in the transport. I have a pristine HDX900-Firestore pkg. that's for sale, if you are interested. Contact me offlist at: