Do you have true Tom Thumbs or just single jointed shanks?
Both. I guess to be honest I haven't ridden in the typical tom thumb for years, unless you count the day I forgot my bridle and had to borrow one from a friend when we trailered out. It was an interesting day, my horse got stuck trying to turn around in the horse trailer, I forgot my bridle, I ended up borrowing a bridle that was an upside down true tom thumb without a curb strap. We did 16 miles that day in a makeshift bridle!
Anyhow, I mostly own things like this: http://www.culturedcowboy.com/images/425.jpg http://www.cowboytack.eu/images/251709.jpg
I know there has been some discussion on how they are not true tom thumbs exactly, because the shanks are a little swept back and such, but still, I can't think there is that much difference to the horse. I doubt they say "hey, wait a minute, this isn't a tom thumb, it's an argentine snaffle."
But maybe I am blind to the nuances.
Lately I have been riding more and more in normal short-shanked ported curbs, because my Fox Trotter seems to like those better, but before I got her the handful of horses I've had have always done better in a broken curb than a solid curb.
I do keep a loose rein at the walk and light handed contact at the trot and canter, unless the horse gets really go-y and then I have to use more contact than I would like (only the Fox Trotter, my Mustang is soft at the canter as well). I also ride two handed a lot. I just trail ride so nothing fancy, but I do pride myself on light hands. I feel my horses are softer and more responsive than when I got them. So I don't think I am ruining them by any stretch of the imagination. Part of that is communication though. The longer you have a horse the more you know what each other is thinking.