Lots of comparisons on previous threads. I've been hammering the Mezzo D9 on a daily commute for 15 months now, having lots of fun and no serious problems (bar one loss of a clip that holds the front wheel in when folded, which I got fixed under warantee, but would have cost me a £5 otherwise).

Benefits of Mezzo, more positive, jaunty ride. No hinge flex. Looks way nicer on the road. Disbenefits - maybe a bit undergeared at top end, but I've only really got irked by that after a year and switched my rear wheel to a capreo hub with 9 tooth cassette. For urban commuting the gearing is pretty much what you need.

Benefits of Brompton - well there must a load, because they are all over the streets. A bit heavier than the Mezzo (at a guess), but folds very slightly smaller. S-variant looks daft for tall folks.

You could - if brave - order an Oribike M9 from Belgium (see recent thread for details). For the same price as a Mezzo in the UK, you get a next gen Mezzo (Oribike=Mezzo in some markets) with hydroformed frame (like the new Birdys). Very fab indeed!