Also had a share in an M20J for a while. All comments so far valid, with the addition of:
1) Relatively little ground clearance for prop, so beware of bumpy grass taxiways.
2) The rudder pedals are a long way underneath the coaming. I am 6ft, and to reach the rudder pedals I had to sit close to the control column, so much so that I could JUST get full and free.
3) The one I flew had no brake pedals on the right, so checkouts were a little interesting.
4) A brilliant touring machine, but required good planning to get it slowed down in time for the circuit if you didn't want to shock cool the engine or cheat by using the gear as an airbrake (some of them have the latter).
If you can get into one, enjoy it. No other basic piston single (and some twins) can beat it on speed.
