The key words here are .... "if used properly". If you do not know what a bitting rig is or how to use it, you could do some damage. I HIGHLY recommend attending some seminars - a lot of the local clubs put them on. If at all possible attend one that is put on by one of the well-known driving trainers. A bitting rig is not something for the novice. You need to know how to use the surgical tubing, how to use the long lines, to know what is a proper head set. You need to know what it means when a horse is "on the bit" or "running out of the bit", etc etc etc. Words on paper (or a computer screen) are not going to teach you how to use it. You need to see it demonstrated and have someone working with you until you get the hang of it.
Watch the Forum and the club newsletters for announcements of seminars. They are WELL worth the time, trouble, and money if you want a well trained (and safe to drive) horse.