BikeRadar has an excellent review of the Extrawheel giving it a final score of 4 stars out of 5:
Running a bigger wheel offers the Extrawheel several advantages. The trailer rolls up and down kerbs and uneven terrain rather than hooking up on to it, so there’s less pulsing when you’re riding. With bags packed to either side, the trailer is wider but the wheelbase between the rear wheel and the trailer wheel is far closer, so the turning circle is a lot tighter.
The other big advantage is that you’re effectively carrying a spare tyre, rim and hub. If these are needed on your bike, your damaged wheel will do for the trailer until you source a replacement. On an expedition tour, I’d run the same hub and spokes for compatibility.
But it’s in its performance that the Extrawheel really impressed. Being considerably shorter than a Yak, it acts as less of a lever on the bike, with much less tendency to try to steer and twist you from behind, particularly when the going gets rough. The larger tyre volume also doubles as a dampener once you get the air pressure right. Hit a speed bump, and the trailer does a single jump, then settles itself down.