I have personally owned a 2008 Dahon Speed with the Radius Inside locking handlepost, and had extensive ride experience with a 2009 using the V clamp handlepost. I can't personally notice a difference between the two.

If you want a solid feeling handlepost, a Dahon using the single piece Syntace VRO handlepost is the way to go in my opinion. I feel as though it is considerably more solid than the telescoping ones.