Ok so first off it’s important to note that there are actually three different bits that are called Tom thumbs, depending on what part of the world you’re in. This is one of the reasons why you’ll see differing opinions on it. In Australia the name is used for a bit that’s similar to a fulmer snaffle (nothing wrong with this bit). In the UK it’s a short shank gag bit that’s the same as what in the US is called a Jr. Cowhorse (which as a gag bit, albeit a mild one, has its own controversy.)

But the American version of the Tom Thumb is what you’ll usually see people referring to, which is a single jointed curb bit (often incorrectly labelled as a snaffle because of the broken mouthpiece, but it’s the shank that makes it a leverage but not a snaffle.) The shanks are straight which makes it automatically harsher with less presignal (though there is a variation with more swept back shanks- you’ll get differing opinions on whether or not that version is actually a Tom Thumb). The single jointed mouth is unstable in the horse’s mouth and with the amount of leverage the shanks give, it tends to trap the jaw in a rather severe nutcracker action when pressure is applied. On top of that, there’s a separate slot for the curb strap from where the headstall attaches which impacts how well the curb strap prevents the bit from over rotating. Overall it is not a well designed bit, there are dozens of other curb bits on the market that are more well balanced and fair to the horse, the only reason they are still so prolific is marketing. Walk into any store that sells Weaver bits and you’ll see one with packaging stating that it’s a mild bit. For years they’ve been pushed as a good transition bit for going from a snaffle to a curb. And there’s certainly people who are still holding on to that concept even though it’s been thoroughly shown to be a mechanically awful choice of bits.

The “soft hands” excuse is never a good one. Because someone with soft hands and a well educated horse should be looking for a bit that is fair and provides more subtle signals to the horse, not one that goes from zero to OUCH! when pressure is applied.