Landing with a flop
You should land at the speed where the pilot still has effective controls beyond that which will be available at the stall all be it that the stall warner should be set to be activated between 5-12kts before the main wing stalls. On a normal landing it is unlikely that the stall warner is activated. Indeed for the aircraft CofA airtest a check is to note that it is NOT activated. I would imagine this particular Swiss Instructor is responsible for a lot of nose leg maintenance as in some types it will come crashing down unexspectedly as pitch authority is lost and no doubt will lead to some very tired main gear when the hold off is a touch too high.
As to the idea that a low slow approach produces a shorter landing is wrong although I know often taught. On an earlier thread a contributor proved the physics that the steeper an approach the shorter the landing distance. The correct approach speed is the most important element.