On my 1440p 23" desktop, things seem to render just fine. On my 11" lenovo helix and on my 15" macbook pro (while running linux), it's definitely noticeable.
I mainly use either Gnome or MATE desktop on Ubuntu. MATE seems to handle scaling the desktop elements better than straight Gnome. But it's still a bit off.
The worst part is browsing the web. Firefox has relatively decent HiDPI support these days, but Chrome on Linux is just terrible. A site like Facebook on Chrome shows the newsfeed as this 3" wide centered column, and you have massive white space on the left and right of it. But reboot into Windows and they make that column much wider and easier to read. On imgur on chrome/linux, I find most of the images are "too tall". If I'm watching an animated gif, I find that one edge is vertically outside of my viewport.
Your only fixes is to change the scaling. As you do this, you start to lose the advantages of the higher resolution:
http://www.pcworld.com/article/2911509/how-to-make-linuxs-de...
Ultimately, things are still usable, video playback is fantastic, but most of the applications really need to improve their Ux on high resolution screens under Linux.
Battery life with Linux isn't great and there were flicker problems, especially with Chrome. Updating the kernel and setting various Chrome flags helped considerably.
EDIT: I should mention I'm using Unity on Ubuntu 16.04
hidpi is not handled well in some (or many) applications, but the window manager (or linux as a kernel) has no problem with it. (and i still have very good eyes)
the usb-c dell adapter works perfectly (hdmi, vga, ethernet), i get up to 8 hours of battery, it's light, solid, quite and fast...
just a bit hot when charging.
the only big issue that i have still to solve is, getting a second monitor to work (mirroring somehow works)... but this is what you get when you don't use a destkop environment and have just a minimal install... (the ubuntu that comes pre-installed has no problems with the external monitor)