Do you have a pic of it? It sounds like a regular curb bit though. As long as he goes well in it, you are able to neck rein him, and you aren't having to pull alot on it, he should be fine. However, if you have to put alot of pressure to get him to stop or turn, I would suggest going back to a snaffle bit, of some sort, as a fixed shank bit (including Tom Thumbs) do not have individual rein pressure capabilities, and all you'll do is confuse him if you try to 'buggy rein' him with one.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."