Whilst on the subject of slipping turns: I fly a cessna 172, and if high on finals for any reason, often use crossed controls to lose excess height. (Please note that I don't do this in the turn onto finals, but when the wings are level).
There is nothing wrong or unsafe with a slipping turn as a technique for losing altitude. I.e., if you know that you are high on the base leg, you don't have to wait until you are established on final before feeding in crossed controls.