I've heard mostly bad stuff about single jointed full cheek snaffles. Everybody says that they have a nutcracker action that hurts the horse. It's not clear with light cues. Horses like to brace against it. It's not good for lateral flexion. Blah blah blah.
People say that the full cheek shouldn't be used because it can get caught on things. They are only for starting young or fresh horses. You shouldn't jump in one (I never understood why they say that...) etc.
My mare seems to go well in her's. It's the first and only bit she's ever had in her mouth, so I can't compare it to anything as far as if she behaves better or worse with it. She seems to be pretty soft in her mouth cues. She bends nicely with it. She tucks her head and does a slower, beginner reining spin nicely. I've never noticed a time when she braces against the bit. She doesn't toss her head from it. The few times I have jumped her in it, she seems fine. Granted, I always give waaay too much rein, so she probably didn't feel any contact.
Is there anything I should know? Do some horses prefer single jointed to double jointed snaffles? Full cheeks to d-rings?
I am training her in eventing. Is there a preferred type of bit for the three phases?