Well, I don't have a problem importing/exporting models that I've worked on in the past, but maybe it isn't a Rebellion-specific issue. The script won't recognize any other mesh regardless of the expansion because it says it's in neither text or binary format. I'm just not sure what to make of that, and it's kind of halted me in my tracks as far as making adjustments to an exiting mod.
The script itself will import and export while rotating the mesh, preventing mirroring, autolinking points, scaling (on export), and tangent creations/options. It also allows you to create, modify, scale, and hide/show points (or arrows) quickly with a single click.
Under the materials option, it seems like it only supports a single data material right now, but it also allows you to easily copy and then manipulate a tangent map as a second material. The lone data material was all I ever needed to worry about, but that might be something that could be easily added.
One of the most helpful elements for me is the Visualization tab, which colors the ship with its texture map, its tangent map, or (what I used most often) the variance map. The variance map colored the entire ship blue while showing any tangent issues in red. So I could quickly identify bits of the tangent UV map that might need to be flipped or adjusted. It's able to update that in real-time, but that option always slowed my machine way down, so I stuck with the manual update. There's a series of numerical thresholds to go along with the tangent and variance values, but I never experimented much with those.
I've also added a dropbox link to the original post so anyone can download the files and take a look or experiment with them.