Walk away from these Dells and don't look back: I had high hopes, but the product quality is just not good.
I have their 24" 4k "retina" display (the only sane size for 4k high-DPI in my view), and the panel at least is TERRIFIC. I hope Apple uses it for a display of their own (they often use the same panels Dell does). I'd love a comparable 5k panel too! A little glow on pure black or dark video, but gorgeous the rest of the time.
But my Dell UP2414Q (styled exactly like this 5k) often fails to turn on when connected to a Mac, and that seems to be a common complaint that warranty swaps don't fix. And the whole thing is chintzy, squeaky plastic. You plug in a USB device and the whole thing flexes. You try to use the menu buttons and some need a harder touch than others. The sensor that lights up the buttons for use goes nuts and starts pulsing a light in your face when you're nowhere near the buttons. The "real aluminum" that reviewers seem to love is actually a BIT of aluminum coupled with a lot of not-quite-matching silver-painted plastic. It's just way below Apple ruggedness and design.
And it generates a ton of heat, has no speakers, no webcam, no mic, no hub beyond USB, and no glass to protect your investment and easily clean.
I wish Apple made a 4k or retina Thunderbolt 2 Display with this same LCD panel. But they don't
I've always recommended Dell displays to others, and their laptops to low-end buyers with a dire budget. I can't recommend either anymore. Just not well-made products.
The UP2414Q has a nice long warranty, though, is priced well under $1000, and when it DOES power on, the picture is spectacular! And has several nice scaling modes--just like a retina MacBook pro made bigger. (Windows-based reviews don't like it because Windows doesn't support high-DPI nicely--and I can say that's very true since I use Boot Camp. Mac OS does it well, though.)