Hi,
I have the Chipmunk 90S and I really love it. I use a OS91FX 2-stroke which provides more than enough power. Probably a 4 stroke would fit the characteristics better, but you can't always buy a new motor!
The plane has retracts. These are really a ... They bend easily and if you don't have a golf green - it's really bad. i am considering changing to fixed ones with a nice original like cover. I saw a beutiful Chipmunk in Oshkosh in the museum with fixed gear. Looks great.
The plane flies great and is not at all difficult to control. It goes through most of the manouvers without any problem. The only bad part are the retracts. You really have to level off, take out the speed and keep the tail down. The flaps really help. Often enough my Chipmunk just tips over shortly before it comes to a stop. Obviously the elevator havn't that much effect on low speed and the gear is very close to the CG. Therefore it doesn't take a lot to tip over.
Otherwise I highly recommend the plane. It looks great and low passes are great. Get it, you will enjoy it.

Rainer