Looks nice (but windows only, I suppose?).
I guess for now it is probably less user-friendly than the official tileset editor, but if I understand correctly, there is already something the official tileset editor does not support: changing the position of an existing tile in the tileset. Integration in Eclipse would be nice indeed.
Remember that many files with different syntaxes have a .dat extension (maps, tilesets, sprites, dialogsā¦), so this is not a general .dat tool but a tileset edition tool.