There is one other factor to this bit that no one mentioned and that is the gag feature. Notice that the mouth piece can slide on the cheek pieces. That creates much more pressure on the poll then a standard curb bit will do. It is much more severe that way and should only be used by someone who knows how to use it properly and has light hands. There is a proper way to adjust it as well. How to Use a Horse Gag Bit | eHow.com
My advise is that since you are not familiar with the bit, avoid it. A properly trained horse will do anything you need him to do in a snaffle. The use of any other bit should only come for specialized purposes and only when you fully understand them.