There's some price discrimination going on here, yes, but keep in mind that a) the PQ on that Seiki will be horrible; 2) at 39" it's way too large; and iii) as you note, it does not have a useful way to get a signal into it.
The win with a ~200dpi 24" 4k will be OS X-style Retina upscaling, not simply screen real estate.
(A) Horrible is a vast overstatement. Unless you need calibrated color, it is fine.
(2) Being too large is relative, my 30" 2560x1600 quickly became normal sized. For the additional pixels the additional inches of a 39" seems about right.
(iii) HDMI at 30Hz is just fine for anything but gaming. I used to have an IBM T221 that also ran at 30Hz and it was no problem at all for text and video. Some people expect there will be mouse lag, there wasn't.
Your monitor's electronics may be doing more processing at 30Hz (like frame-doubling) than at 60Hz thus adding latency that is not inherent in the lower refresh rate.
I used the T221 at 30Hz in a multi-monitor system with the other two monitors at 60Hz. I could drag a window so it straddled the 30Hz monitor and a 60Hz monitor. The DPI was severely mismatched so it wasn't very useful to straddle like that, but movement across the monitors was not obnoxious, not terribly fluid, but not annoying either.
I'm sure different people have different tolerances for latency, but I tend to think my tolerance is pretty low.
a) Not really. Obviously, Seiki isn't setting a benchmark for build quality. But it's also not "horrible." My wife's Seiki has zero dead pixels and is crisp and clear. Brightness isn't even around the edges, but "horrible" is going too far. It's far less horrible than a TN panel, for instance.
2) 39" is not way too large. I want 50" on my desktop.
iii) Yeah, HDMI 1.4 is limiting, but 30Hz makes it still usable for non-gaming. DisplayPort? I guess I won't balk at it, but just give me HDMI 2.
I am critical of the monitor for other reasons: a) it doesn't power up on DPMI on and has a splash screen, 2) it has a semi-glossy screen and professional monitors should be matte, and iii) it's HDMI 1.4.
The win with a ~200dpi 24" 4k will be OS X-style Retina upscaling, not simply screen real estate.