Managed for about 30 years without one, but, like others, wasted a lot of
time farting around cleaning brass by various methods by hand, including
using steel wool with a drill-powered ( and later Foredom powered) 3-jaw case holder collet.
Now that I have one ( I bought the RCBS Vibratory Tumbler) I can't imagine why on earth I didn't do so a lot sooner !
Just gotta have nice, clean, shiney brass ! About an hour & a half with the green corn-cob media, followed by 5 or 10 minutes with untreated "lizard litter" and your good to go. Fair warning though, make sure you do a
one by one inspection of the primer/flash hole ... polishing media gets stuck in there, particularly in the small rifle primer style cases. Just poke it out with a straighted-out paper clip !