Paul,
I just collected the trailer yesterday. The trip home was roughly 150 miles and I found taht the trailer runs quite smoothly behind the car. In Germany, maximum speed with trailers is 80 kph in general, but we can get a 100 kph permission if the suspension is fitted with dampers. So I got these and 100 kph still feels very comfortable.
The fittings like hinges on the top doors and latches are some kind of strong plastic (polyamid?) and I think that this is positive. The plastic is self lubricating and cannot get stuck by corrosion when neglected. I have of ten seen "proper" metal hinges which were hard to move, and then they put bending stress on the base where they are attached, finally damaging the base material. I would expect that these fitting work for longer than their metal conterparts, given that these trailers probably sit outdoors for 20 years or so without much maintenance.
Everything safety relevant is massive steel anyway.
Interestingly, the trailer is fitted with a satellite locating transponder as factory standard now.
Looks fine so far, very roomy, well lighted with glass windows and comfortable. I hope the horse likes it.
Andy