Besides making the brass pretty the tumbler cleans the brass. The brass should be cleaned before it's sized. I don't know what method you use now but lets say you wipe them with a rag by hand. How long would it take to wipe off 600 cases by hand, I don't know I have never done it that way. I would guess about an hour. I can clean those same 600 cases in my tumbler and only have around four minutes of my time involved, the tumbler does the rest. The same with wet cleaning. You will have more time involved than with a vibratory tumbler.
Here it is in short. The tumbler does the work, you do not have to.
Sometimes you get what you pay for, sometimes you only pay more for what you get.
Three shots are not a "group"...they are a "few".
If the Bible is the literal, infallible, unerring word of God...where are all those witches I am supposed to kill? (Exodus 22:18)