BPF, Check PMs.
The A model has two landing flap settings while the B and C models have just the first one which is quite adequate. The extreme landing flap setting in the A model has a rather low maximum airspeed. Exceed that and you are in a noseover
Schleicher got rid of that in the later models.
The 20 is not difficult, but you do have to read the manual first. It's not a club glider.