As far as I am aware, that is a very severe bit. I read somewhere that is has a 'scissor' action on the tongue. Picture an off centre jointed snaffle - there would be pressure across 2/3 of the width of the togue - then put the other piece into the picture...... Also 2 pressure points on the roof of the mouth as well if the joints rise in the mouth.
Having said all that - a young girl has her lesson immediatley after me and hacks to it with that bit in - pony looks relaxed and settled. (bit changed for the lesson I assume, because Grandma walks beside her, with another bit in ther hand).
Horrible thing - it's amplifies a million times the 'harsh' part for a normal single-jointed snaffle- the nutcracker action crushing the jaw and tounge, and the pivoting to hit the roof of the mouth.