Here's my thoughts on a wagon.......
I had a trailer for my touring bike. Big bike with full fairing and a V4 engine. The bike pulled it fine with no noticeable loss of power and surprisingly not even much difference in mileage. It was stable and during all but the worst roads you would not even know it was there. It was bigger than one you have shown in your pics. I would think the one shown would be pretty good as far as size goes. Narrowing it to about four feet or so is good. Don't go too narrow so as to cause instability in corners also keep it the length of the trailer and tongue about the same as the wheelbase in your bike. There is a general rule there but I can't find it right now. I have seen the Bushtec trailers with the bigger wheels and pretty much open frame. Low slung and big wheels looks like it should pull pretty good even behind a smaller bike. I've seen too many bikes too far overloaded and think a trailer with judicious loading would be good.
I'm shopping for a KLR and I think this would be a good match. The caveat to that is I think it would. Pulling a trailer with a bike is no problem but you always have to remember it is there even when you don't notice it. Really no different than driving a cage with a trailer.
Anywhere is home