5b is definitely useful, it's not his fastest poke, but the range and hitstop is decent to use, multi hitter, so the hitbox is good for it's active frames, jump cancellable, if you can score a counter hit, you can do into other thins, but in most cases, 5a is the better option.
His 5a is of average speed, 6f, jump cancelable, 3 gatlings, so it's easy to hitconfirm.
2a isn't that good, it's slow enough to be a nuisance if you're trying to apply pressure, negative on block so you have to commit to a gatling, it's not jump cancellable. Against smart players, 2a won't get you very far.