Answering myself here -- I went ahead and bought a
Plugable UD-6950PDZ, and it just worked fine with DisplayLink (proprietary) drivers, using latest 5.5 Release at
https://synaptics.com/products/displ...ads/ubuntu-5.5 .
Improvements I found, comparing with my (now)previous
Dell D6000 Dock to run 3 external monitors plus builtin display (Thinkpad X1C9)
* run much-o-much cooler -- for the D6000 to be usable I had to install an external fan, to get a more/less stable workday without spontaneous resets
* less frequent resets (have one~two this 1st day trying it)
* coming back from inactivity (monitors output shut-off by Linux) is predictable w/same displays' layout -- kinda obvious you want this, but the D6000 sometimes did completely shut-off the HDMI output, needing a full hard-reset of it
* way more HDMI|DP options, as *each* of the 3 extn monitor ports has both (you need to choose one per port)
* more USB-3 outputs