I remember there was an article in PM recently, saying the EU Regulations regarding towing a trailer are to change.
Again from memory the guist of the article was that a lot of the current "A" Frames may not comply when the new Regulations are introduced.
Take great care with A frame braking systems. Any system that relies on a bungee to stop the brakes dragging is fraught. There are a few American systems which are engineered better than the rest. Those that use bits of pull wire and springs and require regular "setting up" should be discounted.
One owner with a brand new Smart car had it catch fire and burn out driving back from the A frame suppliers/fitters. The case continues as this hapened on April 27th from memory.
Be very wary.