Look, I don't know what % of people have trouble locking a weight out as opposed to getting it off their chest or past a sticking point near their chest. I would guess that, given the muscle fibers are stretched out at the bottom of a press and therefore cannot grab onto each other as well as when they near the fully locked out position that more people have trouble with a sticking point lower in the movement rather than toward the end of it.
Regardless, if you can bench 300 but you can bench 335 with chains, why not bench 335? How is it not beneficial, if you're training for strength, to hold more weight in your hands? All I know is I'm going to gt stronger benching 335 than with 300 if I'm doing both weights for the same amount of reps.
Also, while I've never benched with a bench shirt, I would imagine that using chains is a good way to simulate the same scenario without having to get a shirt. Especially if you compete in meets where you have to lift raw or are a strongman competitor of some sort where you can't use any equipment outside of a belt.