I bought one of the Harbor Freight ones.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93252Its mediocre at best. Honestly. I found that putting a wire brush to something gently for 30 seconds achieves the same results.
I had some stainless steel items that I was polishing and or de-burring. And the thing was... with 8 items about 3-5 inches long, with some sharp edges from turning on the lathe, they took around 12-14 hours to become smooth enough.
Honestly I could have spent about 30 seconds on the lathe with some emry cloth to achieve the same results.
If the items were more convoluted, and difficult to clean and or sand.. then it would be worth it in my mind.
Problems I had... the vibration caused it to have all sorts of parts loosen up.
It also fell over at one point during the several weeks I used it.
Now it basically collects dust as an option I dont use often. I know of options where I would use it.. but I have not needed it recently. I think If I had a slew of bolts and or nuts and things that needed corrosion removed, and or rust, I would break it out.
An alternative I use on Engine rebuilds... I have a 55 Gallon Drum that I cut 1/3 off the top. I put 5 gallons of Simple Green into it, and the rest water. Then I put it on a turkey fryer/propane cooker, and bring it to a boil, then put the engine parts into it via a coat hanger.
After boiling them for 3 or 4 hours, turn the gas off and let it cool to very warm. Remove and voila clean parts.
The liquid is "enviromentally safe" other than the stuff boiled off.