Personally I do not like Tom Thumbs.
Tom Thumb offers a shank with a broken mouth piece, which I find is a recipe for disaster. It also doesn't make sense to me.
So what exactly happens when you apply pressure to the reins with a TT? Well for the most part I would say TT's shanks are 4" long maybe? So with ever pound you pull on the horse's mouth it creates 4 pounds of pressure on the horse's mouth. With ever 2 pounds of pressure you put on the reins you apply 8 pounds of pressure you apply to the horse's mouth.
(How many inches the shank is) 4 x how many pounds of pressure you put on the reins= the amount of pressure thats on the horse's mouth.
Since the TT has a broken mouth piece, it pinches the tongue and hits the roof of her tongue all in one bump of the reins. Leverage bits (like the TT and any other shank bit) encourage the horse's head to drop, while all the horse's I've seen throw their heads up and are confused.
I personally think the TT is NOT a beginner bit to ANYONE (horse or rider). Its too confusing and doesn't make sense.
If your going to ride in a shank, I would suggest this Myler:
This bit doesn't offer a broken mouth piece, a small shank, and a roller. To me this would make more sense than a TT.