I got one of those ultrasonics this winter. I've used a gallon of white vinegar I had in the laundry, a gallon of degreaser twice the price of simple green I thought might be the real deal, and a gallon of Berrymans. Not on all the same stuff for the same amount of time but the vinegar sure cleaned up fuel cap from rust real nice along with a couple other things. The degreaser didn't impress me, the Berrymans isin't the same as the old and although did a fair job it's kinda pricey. I bought a gallon of paint brush and thinner cleaner from the hardware store to try next. About half the price of the Berrymans and same as simple green or similar.
The only thing I don't like about mine is the timer goes to 99 and then shuts off so you can't go off and leave it overnight etc.
I will mention that some parts like fuel filter canisters, oil bath air cleaners, starter,......the paint will all be stripped off as well. Which is ok as long as you don't want to use that same chemical to do a carb or something as the junk will clog stuff up.