Hawk,
I found the Form Master very useful. You don't have to spend money. I built one out of an old strap, some cord, and a few rivets. It works fine and does the trick.
It kicked my butt the first few times I used it. I found out that I wasn't pulling through my anchor during the shot. My bow arm and sting finger should would jump all over the place when I released. I practiced with it for a bit and got to the point where the bow arm and sting finger shoulder did not move when I released. Only then was I was acheiving postive pull thru.
What was unexpected was that the bow started to jump toward the target and out of my hand. My alignement was much better, the bow became quiter, and the speed and stablility of arrow flight are better. All together, the form master is a good thing to try.