Jady,
I have two Lyman tumblers - a 1200 Pro and the slightly bigger 2500.
Very happy with both, had the 1200 about 4 years and the 2500 about 1 year.
Run with crushed walnut shell in the 2500 and corn cob in the 1200, both with a good shot of liquid Autosol - which brings the same results as Flitz or Fliz whatever it`s called, but far cheaper.
The main thing to remember is that tumblers are not cleaners, they are polishers so will not remove built up grime & crap like that.
Anything metal that will fit gets thrown into the tumblers for about a day.
Cheers
Graeme