I love my Birdy, and I commute on it almost every day. As soon as I got it, I installed a 10 speed XT shifter, derailleur, and freewheel. The 10 speed setup gives me a wide range of gearing while keeping the weight down, and it was a bolt-on mod, the 10 speed cog fits the stock Parallax hub fine.

I find the Birdy to be lighter and faster than a Brompton. The Birdy has a more road bike like cockpit, and I can adjust it to mimic the measurements I use on my full-size bikes. While not as fast as a real road bike, the Birdy can still fly quickly.

Besides the 10 speed driveline, I installed XTR brakes and levers, and some titanium hardware. The cheesy stock rims are wearing out, so I will upgrade the wheels shortly. I am also considering getting a better crank set, the stock chain ring works well enough with the 10 speed chain, but the chain guards are too wide, and occasionally the chain slips off the ring and gets stuck between the guard and the ring.

All in all, I can't think of a better folder than the Birdy, my other bikes are getting dusty.