I bought the Radio Shack one, reg. $49 for $29 on sale.
I was fully expecting it to be junk but it's actually been useful.
It's small - my glasses will barely go in. A stripped enfield bolt fits with the handle sticking out. .22 bolts are no problem.
It does a pretty good job of cleaning. It auto shuts off after 3 minutes. Usually have to put it through 2 or 3 cycles.
If you throw a strip of aluminum foil in it, it punches holes through the foil and puts dents in the foil - I read that was a way to test the cleaning effectiveness.
Stuff comes out clean.