Bing! Another common misconception right there - "folding bikes have a short wheel base." Common assumption, seldom true. Folding bikes in general have very much the same wheelbase as "proper" bikes, at around 1000mm. The Brompton is longer than most at 1045mm. Only touring bikes have this sort of wheelbase.

As for the "wobbly" steering, experience has shown that you get used to this very quickly indeed, within one hour, and them forget about it.