I have one. It's pretty. But it provides no useful thing other than occasional touch screen use. But it has terrible battery life. 5 hours is good.
Supposedly the fhd (1080p approx) has much better battery life. I regret getting the 4k screen. For OP above, what's your battery life like? Mine is so bad I keep thinking something must be broken. I'm not doing compiling all day either, doing small things in bash, not killing the cpu, web pages.
That depends on use. For working on or reading papers, it's great: I've significantly cut down on the number of drafts and papers I print, as the screen's ppi is high enough that figures will appear at a similar resolution to what most researchers will have on their printers when adjusted to the correct size on the screen.
I used to own the XPS 9550 (15", 1080p non-touch) and the battery life was around 6-7 hours with the Nvidia GPU disabled. I bought it used so it might have been even better new too.