The differences are described in the link; slightly smaller pan base (just slightly larger than the upper casing) and a new clamp knob arrangement that I can't visualize. We need you to buy this thing so you can post images
(since this is so new we probably won't have any images or a more detailed description until the first samples hit the shop, but I'll see if I can dig some up. If I were you, though, I would order it. If you are unhappy you can return it, but you are unlikely to find anything that fits better and performs in the same league)
Unfortunately I don't have any precise dimensions. All I know is that the Q3T was developed specifically for the Traveler, which would lead one to believe the legs will fold up over it. Otherwise there would be no point to it. When the Shop gets the first samples we should be able to get dimensions, but the proof will be an image of the Traveler folded up over it because there is more there than the base dimension. The two knobs have to behave well too.
Edit: what is the diameter of the Traveler platform?
The differences are the shorter more compact knob (stem) and the slightly smaller diameter base. You might take a look at the Pro Shop illustrations to try to divine which you might prefer. I can't think of any reason to buy the Q3T for a monopod, except the shorter knob stem might make things a tiny bit more compact.
It can be a bit challenging to get the heads screwed down tight on the platform. I use a plastic strap wrench. The differences in the base might make one or the other easier but I'm not sure which (if either) since I don't have them in hand for comparison.