Bearing in mind all the above caveats & that no two a/c are exactly the same, one does in my sort of light a/c rely on the ASI with usually 1.3 X stall for a normal approach.
That's quite a big fudge factor to help deal with all sorts of errors & local wind effects in the airs over the hedge.
Consequently when folk start discussing the finer points of changed direction of airflow - sort of angled across the pitot - one assumes they mean it will read lower than the actual forward speed of the 'plane. They also should simultaneously note that the wing generally sees the same angled airflow.
In both cases the pitot and wing experience much the same net airflow at approx. right angles to the leading edge.
In view of the relative crudity of the pressure sensing system used as a speed measuring device I am of the opinion that when usefully side slipping, if one only keeps to the usual margin over the IAS it a) won't be closer to the stall than normal
and b) one's actual forwards speed is higher, thus requiring a certain amount of care to reduce momentum, restore a normal attitude & a slow enough speed shortly before touch down.
mike hallam.