I was raised using low curb bits so that's what I've allways used.
But lately, I've been trying my two at riding with no bit at all.
They both neck reign, so that part has gone rather well with them both. And my mare responds well to slowing, or stopping, with an equal pull on both reigns. I haven't gotten her to back-up yet though, so that is something that remains to be seen.
My big QH, Charley, is a different story..... he might prove to be too head strong, for controling without one. Like I said, he turns just fine. But he takes his own sweet time about slowing and/or stopping.
I don't know if any of this helps, but there it is.