I know this is the Birdy thread and people like this Bike. I was always eying on it, but before never had a chance to ride it. Maybe I had too high expectations? Maybe I would get used to it after time? Anyway, my impressions after this short ride was, yes, disillusioning. The Birdy's short base and small wheels felt wobbly, nervous, and riding it needs high concentration.
I haven't ridden a Mu but I have owned several Dahons and one thing is very clear: The Birdy quality is way above Dahon's. One quick comparison of the just the handlepost hinge will convince any naysayers.
The Birdy has a strong main tube, where the Dahon has a hinge. Here I like the Birdy (and wish Dahon would go this route and make a truly robust folder available at commodity pricing). In other respects the Dahon quality is just fine regarding the frame and a lot better regarding the parts.
I like the Dahon handlepost hinge: i) it is nicely integrated and smooth. ii) opens/closes in a blink iii) relatively stable, mainly due to conical post shaping. iiii) VRO stem provides quite good lateral stiffness. Very strange that you rate the Birdy's handlepost above the Dahon's. Probably you have a different handlepost?
I think my surprise of the poor riding quality I experienced with the Birdy is due to the following:
a) I am quite tall and heavy (186cm, 95kg). The Dahon has longer wheelbase and more saddle to bar distance. That is the main factor.
b) I probably ride differently than most other folding bike owners? I come from MTB racing. I am an aggressive biker. Sometimes very fast around in town. The Birdy is not designed for this. The Mu isn't designed for it either. But it is quite similar to a BMX feel. It is surprisingly direct, agile, and fast around in town. I like this feel. Stand-n-hammer is no problem. Only I abstain from jumping stairs with the Mu (but hop front and lift back over curbs).
c) the Birdy's suspension didn't please me, particularly the front. It is not stiff. No real damping. It does bounce. It does pivot in the wrong direction (in contrast to other parallelogram suspensions such as the German A or Pacific Reach) giving a bad progression curve (diving effect when braking). It prohibits hands-free riding, which I do a lot on the Mu.
d) folding seems to be quite premature. The handlepost does not come neat towards the main tube. All together it is pretty much the same folded size as the Mu. Although the Mu is much longer (unfolded) and has bigger wheels. Folding speed is much faster with the Mu. Then you cannot wheel the Birdy. It does not stand stable when folded. Quick fold dosen't stand stable either. Rack needs to be unpacked when folding.
e) I have some important upgrades on my Dahon. Plattform pedals, MG1. And last but not least I have 2,35" wide Big Apples on my Mu. These account for a lot better overall ride.