The Reason for a tom thumb bit being so harsh is it combines the pinching of a snaffle with the leverage of a curb bit.
It was designed to be a best of both worlds type of bit and in reality is about the worst of both worlds. From most of the research ive done if you want a shanked bit its best if its not broken in just 1 place like the above and a tom thumb bit.
We have been discussing in another thread myler bits which are broken in 2 places. They are a 3 link bit and reduces pinching. You can actually get a ported bit that is 3 link that is a myler bit and so you also get the clearance of a port with the lateral movement of a broken bit. it looks cool and Im giving serious thought to purchasing one.
But I would advise staying away from tom thumbs and those designed similarly.
"For I know the plans I have for you," declares the LORD, "plans to prosper you and not to harm you, plans to give you hope and a future." Jeremiah 29:11