It's great for my work computer. I develop software and need a lot of windows open. This monitor is great for that. Most importantly, the "4K" pixels span a screen large enough so that you don't need to scale up the fonts via your operating system. (That is a waste of pixels! If you buy a monitor smaller than 40", don't waste your money on 4k because everything will look too tiny.) This 40" display makes text look a bit smaller than my old 24" HD display, but it's OK. I wouldn't go any smaller with 4K resolution.
I do see the red blurring some people mentioned, when moving a window quickly, but strangely I haven't noticed the effect when watching a video, so it hasn't been a problem at all. (Note that the red blur is a side-effect of the LCD tech used in this panel. It comes with both pros and cons. It's not simply a question of good or bad. It depends on your priorities.)
Other reviews complained about the height--about 4" above the desk--but I think it's fine. When I sit in my chair, my eyes are slightly above the center of the screen, so I think it's fine. If anything, I notice a slight darkening on the left or right if my head isn't perfectly centered, but it's pretty mild.
The PIP is cool, but the computer filling the main part of the screen doesn't know a corner is being stolen, so windows and cursors can disappear behind the PIP display. The side-by-side view is probably more useful if you need to hook multiple computers up. Either way, it's pretty cool that these features exist.
Regarding the branding, the AOC logo is applied with stickers. This monitor was likely designed/built by a third party, probably Philips, or who knows these days? The Philips BDM4037UW appears to be identical (at least the hardware), so you can probably buy whichever is cheaper at the time.
The on-screen setup is pretty good, I think. I've never had a monitor with the rear joystick controller before... It's a welcome advance for TVs. A handy shortcut is to press "up" to change vid sources, without having to enter the main menu system. I use that often.
One minor quirk... The audio input has to be from the main video input. I connected my main computer to some nicer external speakers, and so I figured I could use this monitor's speakers as a slight upgrade to my secondary computer's internal speakers, but that didn't seem possible since the sound source options get grayed out when you choose an HDMI or displayport video input (since the audio is usually bundled in those cables). There's no technical reason for the limitation; the menu software is "too smart" to let you attach a random audio source.