They are interesting. I like trying out bikes with weird front ends (I have an Italjet Dragster with single sided swingarm front suspension) so was keen to see what the MP3 felt like, especially given it shares the engine with the 500 Aprilia Scarabeo (a big wheel scooter).
It just felt bigger and heavier all around, not that the Scarabeo is light. With a big, bulky front end due to the 2 wheel set-up and a rather long wheelbase, which feels strange on the small 12" wheels, but does add to the stability.
To my mind, the main advantage for a novice (and for wending through traffic jams) is the CVT. Twist and Go - nice for slow speed manoeuvring.