With respect,
I think it is impossible to see at that magnification what is going on; as to ultrasonic "getting into the grooves," we are really dealing with far smaller microscopic levels.
The traditional factors include transducer power, placement, bath water size, frequency and rotational speed or the amount of time exposed.
As to using a brush, I’ve been "cross-cleaning" for years, using various US machines in combo with traditional manual cleaning and using a point nozzle vacuum machine to remove fluid and/or rinse water.
There’s also the question of surfactants and whether they are effectively removed.
If the question is whether ultrasonic works, I’d say yes, having used both the commercially available machines (before the Degritter): the AD and the KL. As to how to buy, it depends on whether you want one step convenience or are willing to devote more time to the process but perhaps improve your results. You can also save money doing DIY, but that’s only one consideration, and not always the case if you go industrial or medical grade.
I will go the industrial DIY route after the KL dies, not to save $, but to benefit from a more robust feature set while maintaining quality of equipment (Some of the cheap machines you buy online burn out and are disposable).
There’s a lot more than this, but most of the science isn’t applied to vinyl, since US has been used in industry for quite a while for other things. Neil Antin has been working on an update to his original paper on Aqueous Cleaning which should soon be available for free. It will contain some interesting insights into the ultrasonic process, and addresses filtering and pumps as well as the transducers, placement, etc. as applied to the vinyl LP.
Bill Hart
