Unless the volume or parts is tiny don't waste your time on a 18lb tumbler, they work but you are talking 4-6 lbs of parts at best and run times of around 4+ hours.. Also the HF ones only last about 200 hours of operation with ceramic and the bowl wears through and from what I know there are no replacements.
I had a shop-tuff 1.25 cu foot machine for about 8 years. It ran alright but it was pretty small, I would say it is about the smallest machine that vaguely fits professional use.. We did have the bearings wear out and had to order new ones on ebay, and a motor fan a belt and a few of the support springs also wore out.. Also lost the timer to lightning, googled the part number and got a replacement for $1.85 on ebay, the timer is used in microwaves.
Recently went to a Kalamazoo industries kvf3. It is a 3.3 cu ft machine and has a higher weight capacity of 500 lbs. We have been running it for two months and really like it. It is less aggressive than the shop tuff, but the parts are less prone to get damaged in the larger drum.. It is also less obnoxiously loud than the shop tuff.. Note I did not say it is quiet, I said "less obnoxiously loud". You can talk standing next to it without shouting, with the shop tuff it was more of a ear plugs then over ear protectors, and still get a headache from the sound coming in through your eyes.
I process steel parts only, I'm running 3/8"x5/8" ACT DF media from vibra finish. Running 20 gallons of RO water with a mix of VF-100 and VF-RI-8B which is a rust inhibitor for my steel parts, all the media is ordered in from CM topline.. I did have to go to the hardware store to come up with a fitting to get the drain into my shop built water process system.
We are processing the waste water with rm-10 flocculant, using a cordless drill and a mixer wand in a 30 gallon conical tank, once the water separates we drain the water through a 7"x18" 100 micron felt bag which are available on ebay.. The water can be reused for several days but try to change water before it smells like mold, the VF-100 mostly stays in the water, but the RM-10 flocculant removes the VF-RI-8B rust inhibitor, also steel parts deplete the inhibitor with use. When you change water it should discharged after cleaning into a sewer as it will contain some nitrates from the rust inhibitor.