No experience with a mini-sonic tumbler. I use a simple rotary
tumbler - the kind commonly used to ‘polish’ rocks. It’s not
expensive and is very durable. I use stainless steel media with
burnishing compound or a low-sudsing dish detergent. May I recommend
Judy Hoch’s excellent booklet "Tumble-finishing Hand Made Jewelry."
It’s a great resource, practical, and modestly priced. Available
from Rio, among others.
Judy in Kansas, no relation, but a satisfied user.