Do not under estimate the 150/152 spin with 20 flap. Years ago I was giving a PPL with a gung ho attitude to his flying a club check, and I talked him into a 20 flap spin, wich happens very suddenly, and he pulled the stick hard back and tried to stop the roll with aileron. Nedless to say, the 150 kept winding up until I took control. He said to me after that he thought he was dead, then noticed the grin starting to show on my face. The point is, because it was unexpected, he followed his natural instincts instead of getting the boot in. I have been out of instructing for a long time, but I do not think enough effort goes into showing advanced students the subtle traps, probably because a lot of new instructors don't know them themselves. Before any comments are made, I new the guy well enough to know he would not be upset by such an experience, and in fact, he thanked me. Have fun.