Unfortunately the JVCs simply aren't available right now - out of stock everywhere I called, and the one place that had one on permanent demo closed their showroom the day before I was due to visit.
In purely practical terms, the option I had was basically, "want a 4K projector to watch during the current lockdown? It's the Sony, take it or leave it".
I'm glad I took it. There certainly were some PQ issues at first - crushed shadows and an over-sharpened, processed look - but not any more thanks to some adjustments in the menus of both the 590ES and my UHD player. Set sharpness around 30 (not zero!) and Reality Creation > Resolution no higher than 20.
(If you have the Spears & Munsil UHD test disc to hand, I'd recommend calling up the sharpness test pattern and examining the diagonal and circular lines carefully; I found that setting zero sharpness introduced artefacts all of its own, which was completely unexpected).
I'd also add that one of the things I was struck by very early on was just how uniform the picture is edge to edge. There's no banding, vignetting or noticeable loss of focus anywhere across the image. In that respect it's a lot better than my local cinema, which is modern, up-to-date and (paradoxically) also uses a Sony 4K projector.
We've been enjoying a Hobbit 3D session this weekend and the image has been wonderful. Smaug in 3D, setting blazing orange fires in the dark underground caverns, will be my go-to demo scene.