Ultrasonics can offer a lot in getting assembled parts clean.
You can put a dirty part in and watch as the dirt boils off in a cloud.
We watchmakers have used them for many years to allow cleaning watch components without having to totally disassemble them.
Same thing works very well with guns for deep maintenance.
For normal maintenance US cleaners are often slower then normal cleaning, but for the occasional deep clean they're excellent because they don't require actual disassembly.
US will NOT remove copper fouling, and usually won't do a lot for leading, so you still need to clean the bore and chamber.
One thing not mentioned in the video is that ALL lubricant will be removed even from tiny crevices or holes normal cleaning can't get to.
After cleaning and drying you have to get a lubricant inside everywhere both to lubricate and to prevent rust.
One that works well for this is CLP Breakfree because it spreads and creeps into all areas.
The best way to do this is to spray a fine mist of lube, but CLP doesn't come in a fine mist spray, so I have used an airbrush to spray it....(DO NOT breath the fumes, you won't like it).
Also be very careful what cleaner solvent you use, some harsh soaps like Simply Green and Greased Lightning WILL EAT ALUMINUM, and will do it faster in a cleaner.
If in any doubt, test by running a piece of scrap to see if it gets attacked.
For solvents you can buy products made for guns, use hot water and Dawn, or cheap paint thinner.
If you use a flammable solvent NEVER walk away even for a minute due to the fire risk.
In addition to the plastic bag trick, you can use flammable solvents like lacquer thinner in a small glass, plastic, or metal container with an inch or so of tap water in the tank.
The US waves pass through the container.
This allows cleaning and brightening small parts like trigger assemblies.
All solvents work better when hot so either run the tank for a while to heat it up or warm the solvent.
US works better if parts are not laying on the bottom of the tank, use a basket or hang parts with wires.
One caution: KEEP YOUR FINGERS OUT OF THE TANK. US waves and bone marrow don't play well together. This isn't instant, it's cumulative, so just don't start.