First, gotta love those tack catalogs, and even some professionals that use incorrect terminology, thus confuse many people.
Shanked snaffle is one of my pet peeves, and second is calling any curb bit with a jointed mouth, a TT
A true TT, and that deserves all the bad press, has fixed shanks that run straight up and down, thus giving very little if any signal, between the time that the curb strap engages, and bit pressure
There is nothing wrong , using a jointed mouth curb, if the horse rides mainly on a loose rein, is happy and responsive in that bit, and is solid in a plain snaffle, far as leg aids, ect
I would evaluate the horse, using a snaffle, to just see what she knows, and then if she is happy in a jointed mouth curb , no reason to change
I always ride a horse for at least a year in a snaffle, and then move on to a short shanked , loose jawed jointed curb. That bit still allows some direct reining, as needed, and also introduces a horse to slight curb pressure
From there i might go on to a jointed mouth curb with longer shanks or to a curb with a port
Curbs with a port and fixed shanks are for a pretty broke horse
I also collect bits, and have quite a variety of curbs
The function of curbs, is too big a subject to go into, because beside the fact of various degrees of bar, tongue, poll and even pallet pressure, between jointed mouth curbs and those with ports, many other nuisances apply, meant to give slightly better signal, depending on event and level of training of the horse, and the type of bit has to be matched not just with the feel and hands of the rider, but also the education of that horse.
Far as snaffles, full cheek snaffles give a little more signal , as besides rein pressure, those cheek pieces will apply pressure on the opposite side of the face, from rein used
D rings are preferred to be used on horses ridden with some degree of constant contact, and also distribute signal over a wider area than an O ring. Some people will start a horse in a D ring, then switch to an o ring, if showing western
Yes, ideally, even with a snaffle, western horses are never ridden with constant contact, and are shown on a totally loose rein with a snaffle also
Difference being, one rides with two hands on a snaffle and one handed on a curb-western-again-ideally.
Yes, one can ride with one hand on a loose rein using a snaffle,and one can pick up that second rein on a curb, if needed. Again-talking ideally.
I always ride with a loose rein, trail riding, regardless of bit, unless I need to take hold of my horse, and in which case, I also us legs