I'm using both methods, vacuum and ultrasonic (the AD). Love the convenience of the AD, but i also find that with old records- the vast majority of what I buy- I benefit from cleaning first with AIVS No. 15 and lab water, using my trusty old VPI. There are times when the grunge in some of these records requires some soaking, agitation (using a MoFi brush) and lab water rinse before using the ultrasonic machine.
As to the various commercial ultrasonic machines made for records, I bought an AD just at the time the KL was being introduced and have been pleased with its overall performance. Though I was aware that the AD had 'teething' problems, there was little field experience with the KL at the time. (It has since apparently been proven to be a winner).The KL offers the benefit of fewer moving parts and no need for adding a surfactant (not a cost issue, but a potential sonic issue).
So, my punchline is buy an ultrasonic, but keep your vacuum machine for those grungy records. (Added bonus is obviously that you are not polluting the bath used in the US machine if you are sticking a pre-cleaned record into it). The ultrasonic really does change your life if you are used to laboring over a noisy vacuum machine. Unfortunately, it has also raised the bar for 'clean' and made me even more compulsive, devoting even more effort to cleaning with the combined methods.