The Brompton is a much better folded bike (it's a lot smaller, it actually stays folded, it doesn't have exposed greasy parts when folded, you can use it as a shopping cart, etc).
High end Terns (Verge) are more like a normal bike with good components but they are nowhere near as compact when folded (likelihood of walking it into a shop and not getting yelled at is nil, unlike with the Brompton), they don't have as good commuter accessories as the Bromptons and they ride much stiffer (which is good or bad depending on what you are doing with the bike).
I own a Tern Verge myself. Got already > 1'200 km tracked, although not using it that often. Beside some ... issues (a pedal broke, the brakes need some adjustments from time to time and one tire (that I changed myself, I have to add) loses some air over time) I really love it. Especially being able to push it and not having to carry it when it is folded is a big plus for me.
