Sideslipping high wing cessnas with flaps deployed has always been a contentious issue. Some POH's prohibit it, some do not recommend it and some like my 206 POH do not mention the subject at all.There is no doubt at all that a 172 will snap/flick with no warning whatsoever if stalled whilst unbalanced with flaps set, particularly full flap. And elevator and fin blanking has always been an issue. However provided you watch the airspeed, in my view it is still a valid and useful tool no matter what the aircraft