I've ridden one a bit. They're fun. The one I rode had a Kerker exhaust on it, and it was pretty torquey down low, but once you got into the midrange, my EX500 stomped the shit out of it.
That said, it was fun to ride. I really enjoyed it.
As an owner of a Zephyr explained to me, with a 4 cyl engine, you can have any mixture of the following:
You give to one, you take from the other two. The Zephyr gets decent mileage and is pretty low in horsepower for a 4cyl (very close to my EX5, except with a lot more downl-low torque), but it is bulletproof, as was mentioned. I've never heard of people having mechanical problems with these babies.