I've had several 450x's and both were by far the most fun I've had on a bike to date. One was new, then moved, sold it and bought a used one (looks new). If I have the throttle full open in 5th gear, it's time to shut off as I am going wayyyyy to fast.
I have been riding both road and dirt since 1981, and still get an adrenaline rush when riding this bike.
As for the maintenance, change the oil regularly, check the valves and keep the air filter clean, you should have minimal problems...
Gety one you won't regret it...