To cut it straight they are horrible bits!!

You see the bit on most Thoroughbreds, or bigger horses. Because they are strong in the mouth, a Dutch gag, works as a leverage and it works on the pole. As you pull the reins the top ring goes anticlock wise (a lil) so in theroy it pulls on the top part of your bridle. Sara, acually the dutch gag helps get the horses head down, you think if some one puts pressure on you head what do you do? You put your head down to escape the pressure?? Also some ott Thoroughbreds tend to boar (put there head to there chest and just run, you have no control), this bit works to don't let them go under the bit.
I sold a ASH, just recentally and he has to be ridden in a Dutch gag after cattle, he would just get so hyped up you had no control!!
My advice, ask the owner "Why do you ride him in a Dutch gag"?