Tumbers, in Australia you are limited. Locally there is only one brand available. But it works for me. I have had two going most of the day for the last two weeks. I do not over load, a generous handful of parts is enough. Walnut media works for me, but it will stain any plastic parts (slingshot tips). I do not use additives, they have not worked for me in the past.
I do not put in large brackets (pop bumper brackets). Things need to turn with the media, big stuff just sits and bangs on the bottom
Remove any grease on your parts, grease will shorten the life of the media
Media will last for years, even with heavy usage
I bought my tumblers and media from the local gun shop
Lyman Turbo, is what I use
I tried an ultrasonic cleaner. Did not work for me
Plastic parts I either replace, or put in the sink and scru with a toothbrush. Remember to count black stand-offs before you put them in the sink as they can go down the drain