I feel I must speak to what I consider to be less than factual information about bits. Ported bits are not necessarily more severe than straight bar bits. Most straight bar bits put a lot of pressure on most horses' tongues. This makes them very uncomfortable if not downright severe. They cause most horses to open their mouths and many actually fight the bit.
Low to medium port bits never reach the roof of a horse's mouth. Only Very high ports like big spades, half-breeds and cathedral ports reach that high in a horse's mouth and they even don't if the purchase of the shank is long (distance from bit to top ring) and the curb strap is tight.
Snaffle bits are not less harsh than curb bits, especially if a curb bit is used correctly, but they allow a trainer to pull as hard as is necessary to get control. Snaffles should be used on green and unruly horses because a trainer can take more hold and 'muscle' a horse around if it is necessary. Spoiled horses come to mind first here. Any time I have gotten on a horse and it acted badly, the first thing I did was get a shank bit off of it and put a snaffle on it so I could do what was necessary to get control. You should never be in a position to have to pull hard on a curb bit. The horse is supposed to be trained well enough that he responds with a 'signal' of it rather than a pull.
Curb bits give a horse a lot more 'pre-signal' than a snaffle. Any well trained horse should be listening for the pre-signal and not requiring a contact (or at most a very light contact.) Snaffles give very little pre-signal, so most good trainers put any horse the is being finished into some kind of a curb bit so that the horse can be asked for more with less contact.
Correction bits are not harsh. Most professional reining trainers go into one when they move on from a snaffle. Not all horses work well in them, but most do.
Billy Allen mouthpieces were a big improvement over the jointed mouth curbs that collapse on a horse's lower jaw. I do not know any good western trainers that still use them. They are pretty dated -- seen little use in the last 20 to 25 years. I cannot think of one reining trainer I know that even has one, now.
If you want to do any training and two handed riding in a curb bit, (which about everyone now does if they are not in the show-ring in front of a judge), you need to have a bit with completely loose shanks that swivel. This allows the rider to catch one corner of a horse's mouth, lets a rider 'lift' a shoulder, legs a rider develop as much 'bend' 'give' as they have the knowledge to teach.
Most professional trainers do not use shank bits with a single jointed mouthpiece. Those with short shanks do not pinch the lower jaw as much as a longer shanked one does, but they are not nearly as useable as a three piece mouthpiece. These can be ported (like a correction but) or a dog-bone, but they are much more comfortable to a horse and do not encourage a horse to open his mouth.
There is no such thing as an 'regulation reining saddle'. No such thing exists.
There is no such thing as an 'official reining bit'. There are only restrictions on shank length (8 inches) and diameter of mouthpiece and state that the mouthpiece must be smooth, not rough, sharp or wrapped with copper wire, etc. Curb straps and chains must be at least 1/2 inch wide and lay flat.
Horses can be shown in rigid curb bits, like a grazing bit and some of these now come 'spring loaded' with bushings in them that let one shank come back at a time when ridden two handed but the shanks do not swivel around like a true loose shanked bit. There is very little training that can be done in a completely rigid bit.
In our own program, we go from a single or double jointed snaffle bit to a very short shanked 3 piece 'dog-bone' curb. We leave the curb chain very loose when we first switch them over and then gradually tighten it as the horse learns to 'give' to this bit and learns to flex and yield nicely vertically.
When a horse is riding nicely in the little three piece and riding one handed, we either go to a longer shanked correction bit or a medium ported curb with loose shanks and expect the horse to ride on a much lighter contact. When I am riding a 'finished' or a very broke horse, I usually ride in a medium to high port 'Dutton' bit with 8 inch loose shanks. If a horse is going to be shown in 'reined cowhorse' competition, it must go into romal style weighted reins and cannot be shown with any fingers between the reins. Then you have a truly 'finished' horse.
Of all the trainers and programs that I greatly admire, Les Vogt is at the very top of my short-list. Right under him would be Bob Avila, Doug Williamson and Teddy Robinson.