I've struggled with that on other bikes, but the Brommie rack is next to useless, so I'll be inclined to leave it on. Doing my research left me drooling over the Travel-biker as well, but there's no way I'm putting £120 into ANOTHER bag at this point
I think that probably the Office Bag will become my daily use thing for carrying work stuff, and I'll use the T-Bag for overnighting, since it obstructs the light a little.
On that subject, I hadn't realized the Shimano hub dynamo was so cheap. Could have had that fitted instead of the T-Bag, and bought the T seperately (had to come in under £1000 for cycle to work scheme). My battery lights are good, but the rear in particular fouls the fold so has to be removed, and the front is blocked by the T-Bag. I'll live with it this winter, but it looks like it'll cost me £120 for wheel and lights if I want to retrofit, so that might be in my future, though I'll be kicking myself for not getting it at half the cost minus tax to start with.
I'm going to experiment and see if the Brommie wheels fit my Mini Moulton; if they do, then I'll steal the Brommie front for that project, buy a new hub dyno wheel for it, and only have a rear built for the Moulton.