That hitch method on the left bottom single wheel picture looks good as it moves in two planes, but I do not think I would risk any load over say 100kg tops with such a thin bolt taking the twisting loads, especially in Chinese steel.

I just hope the 'single wheel following the bike' method works well against that twist - as otherwise I still think you would be much better off with a hitch that turns around the hitch shaft. I guess you aren't going to be hauling water but I also think that, or any high load, would give you major problems on a bike, ie like water shifting in a barrel and throwing the bike over! I have unfortunately turned over a half empty fire-fighting tanker once ... so good luck mate.