I like the idea of the trailer following the bike in exactly the same manner and attitude as the bike itself, i.e., leaning into turns.
My concern is the twisting torque and stress the trailer would exert on the bike's hitch and frame. The way the trailers are attached to the bike, the trailer is free to turn left and right on the vertical axis at the hitch, but the horizontal axis is rigid so that the bike, when it leans, twists (and holds) the trailer into a lean so that the trailer follows neatly behind the bike. Further, it would be impossible to pack the load so that it is perfectly balanced over the center line, adding more twisting torque (to one side or the other) even when riding straight. Add to that that the load WILL shift as the trailer leans, you go over bumps, etc., increasing the twisting stress.
These are small, light trailers, 85 lbs empty with a 100 lb payload capacity, so maybe that's light enough so that the twisting torque is not an issue. I'm not planning to buy one of these trailers as they are expensive, almost as much as I plan to pay for a Voyager XII but it looks like it would not be difficult to build one.
Just wondering if anyone here has had experience with one-wheeled trailers?

Thanks!