I too have been playing around with ultrasonic steeping. Found this baby on Ebay Paid about $60 AUD for it free delivery in AU.
A friend also has one and has reported that after steeping for 4 x 20 min cycles his juice was good. However two days down the track he tells me that the e-liquid lost all its flavor. Now I am not a chemist, but from what I have I have heard that some plastic bottles will react with E-juice and I suspect especially with ultrasonics. I never steep in plastic bottles nor store my mix in plastic bottles. When steeping with ultrasonic beast pictured above I use glass bottles. It there is a plastic lid I make sure the lid is above the water line.
I did try to duplicate my friends problem using a plastic bottle however nothing to the contrary happened and my juice is still good. What happened to his juice I have no idea. We both used the same VG, same concentrate and the same type of plastic bottle to try to duplicate the problem.
Has any one had any such problem?