I’ve had an ultrasonic cleaner for fifteen years or so. In that time it hasn’t had a lot of work because I’m unimpressed with it. The one area I found it useful is with oxidation removal. Otherwise I go straight to full disassembly and cleaning with brushes. It does a better job. I’ve run parts through the ultrasonic, taken them out and removed more ink with a brush. That’s the test for me.
I only used it in the repair process. Some use the ultrasonic as part of their flushing of the pen. I wouldn’t do it that way, especially with hard rubber sections as it risks discolouration.
I suppose things have moved on in fifteen years and maybe small ultrasonic cleaners are better than my one. I hope so. I know that the bigger machines used for carburettors and other components work well.
What do you think?
Goodwriterspens's Blog 
Hi Deb….just to play devil’s avocado….I must say , notwithstanding your excellent advice which I discovered early on from reading this blog, about not soaking hard rubber or caps , I have been amazed by the efficacy of my little machine.
I have no problem with knocking out feeds and resetting etc in order to repair nibs ( to the extent that I’m proficient 🙄) and have found that whacking all the bits ,minus the section itself if it’s hard rubber, in the bath has been a really great way of cleaning in places and with an efficiency that was often better than I could achieve by brushing.
That said, I doubt I’ve got even close to the experience you have, and may yet to come across instances where it isn’t a good idea .
…seems to be one of those ‘some do some don’t ….whatever gets you through the job’ things 😎
I do like “devil’s avocado”. I’m glad your cleaner is so useful for you.
As a general rule, I never put hard rubber into water. I’ve had one bad experience after another. I will run metallic or plastic parts through. Usually, caps to help remove the old dried up ink from the inside.