Record Cleaning Machine ~ Ultrasonic vs. Rest

My experience- it is not a "vs" but an "and"- the two different processes, manual cleaning with vacuum and US are complementary. Sometimes, you really have to work a record in the manual cleaning phase; I always use a rinse step and since I don't use chemistry in my KL US the bath water stays cleaner as well. 

When I got my first US machine- an Audio Desk- some years ago, I found certain records remained noisy. That's what led me to go back to manual cleaning and vacuum. (I buy mostly older pressings). 

If your collection is largely pristine audiophile quality pressings, you may be able to get away with US only, but with used records, I found the combination to be much more effective. I never used the Project; I had a VPI from the early '80s that was still working fine when I gave it to a friend in 2017; I use a Monks Omni (traditional point nozzle with thread). Like @dogberry that's one machine I would not give up. 

If the water bath in a US machine stays “clean”, doesn’t that suggest it’s not removing detritus from LPs, which is its purpose?

It's a question of how clean, isn't it? I use a cleaning solution with surfactant on the Loricraft, followed by a DW rinse. Then the Degritter with just DW, relying on cavitation for any further cleaning. Since Degritter recommends changing water every 20-30 disks, I'd rather remove the majority of crud with the vacuum machine and not contaminate the Degritter's tank with any more of it than necessary. If I changed the water after every disk, which might seem the counsel of perfection, I'd be running my water distiller every day to provide enough. Just a matter of finding a trade-off that one can be comfortable with.

The compact ’keep on a shelf’ design appeals to me, anyone tried it or one like it/

HummingGuru 40hz clean/dry

Dogberry, so far as I have been able to learn by reading the many threads on US RCMs, you are correct not to use a surfactant or detergent with your US machine.  As far as I can determine, most manufacturers of US RCMs don't recommend adding anything but water to the bath, except maybe Kirmuss with all its pre-cleaning rituals. But I think that using detergents/surfactants, as I do in my lowly VPI 16.5 or 17 (not sure what I have; the platter rotates in both directions, and it has a stainless steel waste tank) is a decided advantage in favor of the vacuum type cleaner.  My neighbor had a Loricraft for a while, but he kept having problems with the string thing.