I have a Burley Travoy trailer that I've used with my Brompton, and so far, I'm pleased. First use was picking up a load of household items at Ikea Brooklyn and cycling back to northern Manhattan by way of the Brooklyn Bridge. There was plenty of maneuvering through city streets, potholes, and the like, and the bike + trailer handled it fine. I've used it since for groceries, and it's been good. The Travoy seems specially made for the tight turning that urban cycling requires.

I'm even thinking of using it for cycle touring where my wife and I carry our front Brompton bags, and I'd add the trailer to carry our camping gear.