Today, a man in the gym told me that it is useless to do more than one type of shoulder press exercises. I do two exercises, one with dumbbells and one with a lift. Is he right or not?
Doing more than one shoulder exercise for increased hypertrophy is perfectly logical.
However, there's a diminishing return on how much hypertrophy you can achieve by simply doing more of the same type of exercise in one session.
So for instance, if you've done 3 sets of barbell OHP, followed by 3 sets of dumbbell OHP, I don't see a problem. But if you're doing 10 sets of the first, and another 10 sets of the latter, that's definitely overkill. You might achieve more muscle growth by splitting that up into shoulder AND chest for instance.
If you are talking about Over Head Presses, I would suggest against doing them, reason being Shoulder Impingement and restriction of shoulder moment due to shoulder biomechanics. Shoulder doesn't performs the function of pushing the arms upward. Rather shoulder raises, front, side and back would be more beneficial without any negative effect. Please look at this video.