Currently only using one Ultrastudio MiniMonitor, running the firmware that comes with Desktop Video 11.3, last update 18. July 2019. I wouldn't call the Ultrastudio product line converters because they're proper video interfaces, like the Decklink PCIe cards. And because Blackmagic also builds actual converters (HDMI-to-SDI etc).
I'm pretty much convinced the main problem I'm seeing (Prores files not playing back so reliably; see above) has nothing to do with the Ultrastudio output, given that GLSL shaders play back near-flawlessly.