I remember Dougie King from my famil flights in the T53 (Halton about 1970). Dougie sat in the aircraft literally all day. On my flight, I quickly discovered it suffered from fearsome adverse yaw; not only did I have to use gobs of rudder to make it turn, but I could feel Dougies feet pressing into in my back every time he turned it.
As someone said earlier, it was Slingsby's answer to the Blanik which could not be purchased by MOD because it was built in an Iron Curtain country.