It's hard to compare it with a Brompton...
It's folded shape & neatness can't compare to a Brompton
I would put their ride quality as close to each other; the Birdy is better wrt fitment.
Comparing the old and new:
My colleague has a Birdy with the older frame. I couldn't say that the difference between the working bits between the two bikes are much different.
* The seat clamp design of the old one is not so great for working with the folding rack. It works, but it is one of the things they abandoned in the current design. I am unsure if the design prompted it or price. Certainly the current design is heaps cheaper.
* The steering riser clamp design is slightly different, mainly aesthetics.
* Geometry is same
* Fork design is very close to same
I wouldn't say there is that much to choose between the two. Wear and tear will be more telling. Check the hinges for play.