I believe the monoque is light and a bit smaller - but it could be my mind playing tricks.
I love mine - it's perfect for me and I ride the street version of trails going through Bushwick and Williamsburg to commute to Manhattan (very industrial/full of pot holes).
Marathon racers are pretty solid for this but might not do as well on a trail. I hear the Pocket Rocket is a good MB substitute, but not sure how small it folds. I took a friend to Bfold where she got a Brompton, and I have to say that while the brompton is amazing compact, the Birdy is not to shabby and is a great bike. Wow does it accelerate fast.
As for the tires, they are hard to find. No idea about getting MB style treads.