The bit is primarily a communication device. It transmits the rider's command from the hand to the mouth. It is not intended to be the only "communication device" but it is a primary, natural aid (the three natural aids being hand, seat, and leg).
Clear communication of rider desire will mean improved equine performance. The horse that understands a command will perform better than one that doesn't. This should be intuitive with any rider and even more so with any trainer. Adding power to the bit does not, necessarily, add clarity; it may just add volume. Add other functions to the bit (like elevation of the head, lowering of the head, etc.) dilutes effective communication and that, by itself, can lead to a lack of "clarity" to the horse.
Pick the bit that best communicates with your horse. One bit does not serve for all horses. One class of bit is not appropriate for all disciplines.
Regarding the "one rein stop," it is grossly overvalued as an "emergency brake." It will work only
if (1) the rider is correctly trained in its use and, (2) the horse is trained to respond to it. You haven't lived until you've been astride a horse that is bent to the left in the shape of bow with it's nose **** near up its butt and is moving sideways to the right at a high rate of speed (and can't see a **** thing in that direction). Ask me know I know.
Effective, lasting equine training takes time. It requires intelligent repetition (meaning that the rider is consistent in their use of cues and aids). It's not done in a day (much less in a few hours, a la
the abomination called "The Road to the Horse"; getting a youngster started as a race between ego-laden gurus is a fine way to ruin a good animal).
Col. Alois Podhajsky (former Riding Master at the Spanish Riding School) had a mantra that went "I have time." Any person who does not have time needs to exchange their horse for a Harley.