The C152 would, if side-slipped agressively with full flap. achieve remarkable rates and angles of descent. Some precision was needed to straighten up without losing some control and immediately land gently at an aiming point close to a notional hedge, in a practice forced landing. Fishtailing was an acquired art.
The whole aircraft would buffet a little if pressed hard enough, but there was no loss of rudder/elevator control during the slip.
As far as I can remember, it was advised to use the elevator to keep the IAS 5-10KTS above the full flap, no power, level flight stall speed.
The Auster was similar, but with slightly less powerful flaps.
I guess that the thinking was that the actual net velocity was immaterial, and that if the pitot head, meauring the forwards component, showed that this component was well above the likely stall speed the wing would probably keep flying. I now wonder if the pitot location (ie which side of the fuselage) made a difference.
No doubt an expert aerodynamicist can explain better, and indeed one already has, to an extent.