zhijiang,
I flew a Nexstar a couple of weeks ago....in my opinion, it was OK, but not great........we had the AFS stabilization unit turned to considerably, and the plane still wanted to right itself too much.......I didn't like the fact that turns required me to hold the stick in position......that's a bad habit to get used to........also, I did a roll with the plane, and during the inverted stage of the roll, the plane almost put itself into a spin....it took me by surprise....I think it might have had something to do with the speed brakes/flaps on the wing. Like I said, the plane was OK, it flew good, but definitely not the best trainer I've flown.....the engine was great however. If you have an instructor to help you out, I would probably go with a different trainer.