Ultrasonic LP Cleaning vs. “Thread Type” Cleaning (Keith Monks/Loricraft/etc.)

I use a Monks Omni-basically a reboot of the original Monks with some refinements, in combination with ultrasonics (like Mike, I have the KL, which has -knock wood- continued to function well though it is not new).
If I had to choose one machine, it would probably be the Monks. I do a wash cycle with different fluids depending on perceived need and a rinse step using high purity water.
The ultrasonic step adds another dimension to this which I like very much. I can use the ultrasonic alone for new records but for older grotty copies which have ground in contaminants, I find using something like AIVS #15, soaking and agitating, followed by a reagent grade water rinse, removes some distortion that ultrasonic alone did not. I encountered this several years ago on some high value collectible records, and since then, have employed a double cleaning method utilizing both.
Ultrasonic cleaning can be enhanced through the use of surfactants to lower surface tension of the water and increase cavitation effect. The biggest issue is then the removal of the surfactant after the ultrasonic process (if you are not using water alone in the ultrasonic machine). Some people are more sensitive than others to the residue left by the "cleaning" fluids-- here again, an extra rinse step helps.
If I were going to do an ultrasonic after the KL, it will likely be an industrial grade machine that is adapted for use in cleaning LPs, rather than a made for LP ultrasonic machine. This is not a cost-saving approach, though you can buy ultrasonic baths and the necessary equipment to rotate the records cheaply enough to put DIY ultrasonic into the "bargain" category. Instead, I’m looking for a more robust design, multiple frequencies, ease of cleaning the bath, filtering of the bath water for contaminants (not to filter out the surfactant), degassing and other features that tend to be associated with industrial ultrasonic equipment. The better med/tech machines, like the Elma, offer a lot of these features. The Zenith company, which builds full factory lines with multiple baths, offers a bench top (thanks, Neil!) that has an external power supply and is apparently built for industrial, not medical equipment, usage.
For what it’s worth, it is my impression that the high end community jumped on ultrasonic record cleaning largely due to convenience and got good results--many such users probably have new or pristine copies that were collected by audiophiles and ultrasonic alone may be sufficient for these. The more DIY ultrasonic approaches are less convenient than a one button "pop it in the slot and wait til the bell dings"- but offer more for someone who is crate digging and finding those jewels that need more attention. I’m not a Goodwill/Thrift Shop type record buyer, but rather someone who buys old private label and more rarefied jazz, hard rock and prog, dating back into the ’60s and earlier. Unless you find a sealed specimen (rare and has its own risks), you’ll likely encounter a record that needs some attention to achieve a high state of play.
PS: at the risk of exceeding my welcome by prolix prose, I also find that the vacuum of a record at rinse stage using the point nozzle type vacuum cleaner is more effective at removing residue and contaminants than the forced air drying typical of the "made for LP" ultrasonic cleaners. It sounds like a lot of work, but my processes have been simplified and I can roll through a stack of records in short order. I tend to clean in batches.
Oh, I had a VPI. A 16 that was converted to a 16.5 that I bought in the mid-’80s. That thing would not die. I gave it to a friend when I moved.

I thought long and hard about a US machine and decided against purchasing because of all the potential issues and "work" involved, at least as I see it. I would worry about US actually damaging LPs, as rightly or wrongly claimed by some others. One wants to avoid that, so what frequency for what amount of time is really harmless? What amount of heating is harmless to an LP? Can you use detergents in the bath water? Some do; some don’t. The effluent from my VPI HW17 is filthy, which makes me think I would want to change the US bath water very frequently and/or filter it via an external circulation. When all is said and done I decided to stay with the HW17, which by the way never overheats. I also use Walker Audio enzymes for really dirty LPs and combine that with a distilled water rinse using my VPI. This is purely to illustrate my own thought process and not to say that anyone else’s choice is "wrong". I also had an opportunity to purchase a string type Loricroft cleaner and was put off by the maintenance issues as described to me by a Loricroft owner. I don’t see why it would necessarily be superior to the HW17, and the HW17 presents fewer headaches. I clean my LPs in my basement workshop, well away from either of my two systems, and don’t care a fig about the noise from the HW17.

The Keith Monks is the original RCM. Used by Better-Records, BBC, Library of Congress, etc., etc.
After decades of refinement, the KM RCMs no longer use the maintenance heavy string method. The nozzle vacuums off the dirt with a medical grade German pump. The KM fluid is also special.
The fluid is easily applied and quickly brushed in. The whitish surfactant is seen. The arm is placed on the label and automatically travels one grove at a time as the nozzle vacuums up all the dirty fluid. This takes a bit over a minute a side. Quick and complete.
As opposed to several minutes for the US machines and the records sitting in the dirty water.

@mglik - I think the maintenance and care of the "traditional" Monks is overstated. When I got mine, used, I knew it was not performing as it should and had it rebuilt by the guy who does the institutional work for Monks based out of NY. He also showed me how to operate it properly and we made a few tweaks- he repositioned the "arm rest" and I added silicon washers wherever there is metal to metal contact on a screw. (Some of the old Monks show rust- frightening). Once you get the hang of it, it’s relatively easy to adjust and maintain.
I don’t use the fluid applicator head since I use a variety of fluids and I found that the dispenser flings fluid beyond the platter-- I keep a microfiber towel handy to wipe the surface as it is running, and once done, use some canned air to get water out of any crevasses, empty the waste jar, cut off the "used" thread that has been sent to the waste jar, etc. The machine wipes down easily and threading the bobbin, while not easy, is something that an owner can do with a little time and trouble- it basically involves taking the nozzle off and re-threading the "string" through the arm tube using a little rubber pipe that then allows the vacuum to pull it back through to the waste jar. You can clean a lot of records with one bobbin of the special thread.

Some of the machines may have been abused (commonly, too much waste water without emptying the jar will cause water to flow back to the diaphragm of the pump and then the diaphragm has to be replaced, if not worse). Even with a rebuild, mine came it at less than retail for a brand new Omni. The older models can be brought back to life at some cost. I would recommend that anyone buying an older Monks have it checked by someone who knows the machine. It was an ingenious sort of Rube Goldberg affair when it was first made, and has the quirkiness of a British vintage car, sans the Lucas Prince of Darkness issues.

There is a huge variance in US cleaning machines. Your question is rather like asking if a car is faster than a bike.

As @whart has noted, US results depend on frequency, power, temperature, spacing, surfactant, and rinse. It’s only when you get careful with all of the above that your results approach optimal.

The first question to ask is how much you can trust your US bath to meet spec. If it’s medical equipment from Germany, you can trust it a bit more than flimsy-consumer easy-to-use from anywhere.

There are threads on this topic which you might want to examine. A high class expert on cleaning technology, whose handle escapes me, contributed to one thread and refined my own cleaning process, for which I am considerably grateful.

I use an Elma US machine from Germany, and doubt very much that my records are less clean than anybody's.