ive used citrix acid in my ultrasonic cleaner to good effect on small parts , leave it to soak overnight then run it in the morning to clean the surface off then repeat until rust gone
I too have used my ultrasonic bath on rust, with a solution of citric acid and a drop of IPA as a wetting agent. Depending on what you're cleaning, probably a good idea to keep an eye on it.
for me it seems to clean the rust off the hard to reach places, plus when you take it out if its running the water hot it drys really quickly and put it straight in dewatering and rust preventing solution
ive used my fathers for stuff with surface rust, and caked on crap, we used carb cleaner to get the crud off and then used cleaning vinegar for anything with excess rust, seemed to work reasonably well but still needed a bit if scrubbing to get it all off