We had two, made by Adams I think. I wouldn’t recommend them for the simple reason that the hitch allowed the trailer to flop from side to side, which was extremely disconcerting for me as the engine. It has a strange arrangement with a tapered block for joining to the hitch, which is never tight enough to prevent movement and there’s movement in the other parts of the system as well.
On one occasion I was pulling away at a roundabout and I set off less than smoothly, jerking the bike to one side a little. The exaggerated movement of the trailer caught our child by surprise and threw him off in front of a car, which luckily stopped in time.
So in my opinion the first criterion for buying a tag along should be the design of the hitch. The rest doesn’t matter as much!