I've found this thread quite late, but one thing I would like to add is that the cleaning solution used can make a massive difference so its well worth looking at what is available.
My experience is with small 5 ltr tanks which I use for cleaning clock parts, I normally use an ammonia based solution called horolene that you dilute with seven parts water to one part cleaning solution. That solution is good especially for brass and steel, and you'd be amazed at the results it will give on items coated with over a hundred years worth of oil, dust and grime in just a few minutes where a day in the tank with some homemade solutions will barely make a dent in the cleaning.
Anyway, these cleaning solutions are expensive and probably not generally suitable due to cost for basic cleaning, but for more serious cleaning well worth a look at.
One point of note, any parts such as springs that are
under tension generally do not like the effects of ultrasonic baths and will suffer breakage not long after cleaning.
Anyway, here is a before and after of a 70 plus year old clock movement that was simply dunked in a proper solution in an ultrasonic tank for five minutes, not best practice as really you pull them down to individual parts for cleaning and repair to worn bushings, but this was done to show the effectiveness of ultrasonic cleaning with the correct fluids.
