I'm toying with the idea of getting one. The ones on Amazon (UK) generally get rated at less than 4 out of 5 stars, with quite a proportion of 1 and 2 stars.
I have picked up a Samsung 28" ultra HD Led 4K monitor 2 weeks ago an have been very impressed with it. I was trying to decide between this one and the ASUS 4K and decided on the Samsung with the price point being slightly lower. I have it running with gtx970 OC SLI cards and get a rock solid 60fps via display port (HDMI is limited to 30FPS).
the ASUS display uses display port for 60FPS so make sure your video card supports this too.
Very good for the price. The build quality is great and minimal. The screen is lovely to my eyes. I have one running at full 4k and the other one step down and my card runs the just fine.