The tfil will only help those having issues updating the game because they cant download torrent files. It cannot be converted into a regular torrent file and cannot be opened on a bit torrent client.
Many Colleges/Universities block all sorts of P2P download including BitTorrent. This is a way to bypass their firewall and allow your World of Warcraft to update. However, after downloading the tfil it's recommended that you disable P2P transfer on the Launcher options to avoid breaking their rules on P2P usage. Other public/shared networks may have the same restrictions on Peer to Peer downloading.
Instructions:
Select a region above.
Download the tfil.
Extract the file and place the Diablo III.tfil in your Diablo III Beta folder.
(Download the Diablo III.tfil, not the mfil)
That's it. Now open the Launcher and let it update.