My mare rides in a Little S Hackamore. It's a type of mechanical, but it's much gentler than the typical hackamore. My mare does go in a bit but she hates them (was a commercial trail horse for a few years) and going in the little S is a night and day difference, she works so much better in it - calmer, her cues are lighter, etc.
The downside is that I don't think she has as much "whoa" in a bad situation. There's been one situation on the road where she was in a blind panic (we were waling at this point, I wasn't riding), and the ONLY thing that let me keep a hold of her was the reins on her bit having enough bite to keep her from bolting into the oncoming traffic. If it was the hack, I have a feeling she would have plowed right through it - shes wonderful with it when she's calm but I think if it hits the fan it won't have that bite to stop her. Nose pressure doesn't come through that panic as well as a bit, and I don't want to use a mechanical with longer shanks when she doesn't need it.
Of course the solution to that is to train her better, but you never know what could happen. So, even if she goes amazing in the little S, if we go somewhere that could cause issues she'll get ridden in a bit - at least for now.