I have the P2715Q and it's an awesome display. It has a pretty decent OSD too, which is not only functional, but also looks clean.
I just bought the U2718Q and the OSD is shockingly bad. It makes the monitor look low quality. When I first turned on the monitor, the logo and text are so pixelated they are borderline hard to read. The kerning and font rendering is super ugly.
I don't understand why a 4K monitor doesn't have a 4K OSD that actually looks good. For the price of this monitor, it's a bad first impression and very disappointing.