A bike that fits you well and is mechanically sound will be a decent bike regardless of it's wheel size... my P20 measures out just like my other bicycles fit wise and has seen a great deal of commuting (300 miles a week in the summer) over the many years I have owned it. It was so comfortable and carries weight so well I decided to turn it into a touring bicycle.

I do not feel like I am giving up anything when I ride it.. it is quick and agile and comes off the line very quickly which is great for stop and go city riding. The beefy 406 wheels and 1.5 Marathons can handle the worst of roads due to smaller wheels being proportionally stronger.

Brake wear is higher on a smaller wheel due to the increased wheel speed and if you ride a higher performance model of folder or small wheeler you will appreciate better brakes as energy is a function of mass and the square of velocity... that smaller rim will be spinning much faster than a road wheel and has more energy to overcome.