I tried it - it’s okay, but a bit flaky - especially disconnect/re-connect. While it does _improve_ font rendering on sub-Retina displays, it’s still nowhere near as nice as font rendered on a display recognised as Retina-capable by MacOS - which any 4K display is. It’s particularly noticeable in the setup described above, as your eyes are constantly moving between the in-built Retina display and your external display.

It might be a good solution if you already have an, eg, 1440p display and want better font rendering, but if you’re putting together a setup from scratch, MacOS just works hassle-free with 4K displays. You’ve got to stare at these things for hours every day, so.