An acquaintance of mine has a Third Wheel Trailer. He and his wife, my wife and I (along with our Uni-go) and a couple of other bikes did a two-week ride from Vancouver, BC to Utah a few years ago. in addition to the great scenery of Utah, it provided an opportunity to see how the two single wheeled trailers performed side by side. Each was connected to a 2-up GL1800.
The Third Wheel was new to the other rider and this was their first trip with it loaded up and with full weight on the bike.
The only real problem they encountered was with the stabilizing stand, under the draw bar. It holds the trailer upright when its not connected to the hitch.
At the first gas stop, the stabilizing stand dragged leaving the gas station and one of its little feet torn off. Even after being made aware of this potential drag point, the stand was twisted and bend a couple of days later. As a side note. I looked through the picture gallery on the Third Wheel sight and noticed many of the other trailers did not have the stability stand. Its removal resolves the above problem but would make it challenging to keep the trailer upright when not hitched up.
The only other design issue that had a direct impact was loading the trailer and keeping the contents in place. The shell splits about half way up. When contents are loaded they need to be stacked and may want to fall off or get caught in the seam while closing the lid. The acquisition of a cargo net resolved that problem.
Both of the above were relatively minor and any other issues where personal perception. I personally did not like the very visible frame underneath as it had a significant impact on the unit's visual appeal. Whenever other bikers gathered around at the evening's motel stop (ofter), most of the attention was on the Uni-go with comments referencing it as a more sophisticated and finished design.
The other rider did not feel comfortable at speeds above 75 mph (nothing to do with the trailer) so I cannot comment on how it towed at high speed. At the speeds we traveled, both the Uni-go and Third Wheel worked equally well.
The Uni-go looks better and its design is more refined (IMHO) but it also costs more. There is nothing significantly negative about the Third Wheel that I am aware of and if you want to save a few dollars, it is a viable alternative for a single wheel trailer.
As a side note, as things may have changed in this regard, I had some quality control and delivery issues with my Uni-go and the Third Wheel owner had delivery challenges from that manufacturer as well.
