That's a popular tumbler.

I use a GRAF (re badged Berry) and I swear by it. I've used it on over 50 machines - and it keeps going. I'm thinking of buying a second.

Make sure you wash any dirt / grime / rust off the parts you want to tumble or your media will quickly absorb the dirt residue.

I used corn cob with Flitz (from the USA). I've tried Brasso and Novus 3 - no where near Flitz - and flitz takes half the time.