I was able to get it working, but it turned out I only needed the USPS online mode, and it was simpler to post XML directly to the post office site. If one's needs are simple, this can seem like a lot of module. Can't comment on the overall performance since I did not end up using it in production.
I did find the docs a little sparse. For instance, when you initially communicate with the USPS server, you're required to do so in a test mode. That's supported, which is good, but the switch doesn't seem to be documented outside the code itself, so it took me a while to find it.