I used to borrow my friends all time time and it was fantastic. I love them and swear by them, and in my own experience they are just as safe as any other horse trailer. They are so much lighter to pull and in turn, with the help of the electric breaking system, stopping is much easier and more fluid than a traditional trailer. I have a brand new 2012 Circle J 2horse slant, alumninum skinned trailer with electric breaks, but it still takes me FOREVER AND A DAY to stop. Which means that when some one (enevitably) cuts me off its easier to stop or avoid accidents.
I will say that Brenderup is no longer in business but I'm not sure why, so the availability of parts, repairs and service in the future is unknown.
That being said the Brenderups are clones of European trailers that are now starting to make headway in the US. There may be some crossover but the field is new and uncertain.
I would say evaluate it like you would any other trailer, including future maintenence.