My dual drive mezzo 21 speed with bullbars and a spare suspension seatpost is on ebay at the moment if you are interested. I would make sure you get a spare seatpost clamp if you do go for a mezzo. Spares are getting more difficult to find but it takes many standard parts.
How small does the OP fold need to be?
I would recommend a 20 inch over a 16 inch for riding ability, if you dont need the small fold. A birdie with big apples is very forgiving on rough stuff.
Another left of field option is the bullet proof Diblasi R22. Smallest fold of the 20 inch bikes, but not the best qualisty for the money.