You are right it will tell you if he is deceptive but not neceswsarily his mechanics. The ball is being thrown to 1st and you can get a better look at mechanics in my opinion.
Son learned to throw without looking at 1st. Taught to know where 1st is by feel. One pitching coach had him pitch blindfolded in winter classes.
My son looks at home plate as he stepds towards 1st on the 45 angle and he throws with pop to 1st. If you can pick 6 guys off in 7 innings at a high level you are doing it right. Once you get 1 or2 they are ready for you.
This young pitcher can evaluate what is said here and pick what he likes. He acknowleges that he needs some pop on his throw and I told him my suggestion on how to get it. I have seen many different LHPs with all kinds od deceptive moves and they all have developed some pop.