I have used them on water damaged iPhones and my wife's jewelry--not comparable, I know--and was really impressed. There's one on Amazon for about $30 that has great reviews, and that's what I bought. It wouldn't fit a whole gun, but it'd fit a Glock slide, for example.
I clean cases for reloading and it does an excellent job inside and out in about 4 minutes. I've not used it for gun cleaning although I think it would work just fine. I've got my own formula for my cleaning solution.
ETA: I bought mine from Harbor Freight considerably cheaper than the exact same models the reloading manufacturers sell.
The cheap Chinese HF models will work, but probably won't last long. I've got a couple of friends who work on higher-quality units like L&R (they do repairs on them because these are commercial grade). They hooked me up with a refurbished L&R. Works great. Weak anodizing and some paints and coatings may come off in the cleaner. It won't take out lead or copper fouling in my experience, though. Otherwise, they do a stellar job of cleaning guns and parts.
I also used mine on some really gunked motorcycle carbs a while back. Half an hour in the cleaner and they looked like I'd soaked them in a fresh bucket of chem dip all day.