Works good, rich and highly configurable firmware, has much more configurable options than any other mainline vendors motherboard. Quick boot and all first impressions are only good. Negative sides: firmware can be updated only by physical chip programming, VRMs heatsink is terribly hot, looks like it need some handwork on better cooling. Been able to install macOS on it, but not Big Sur, it's installer fails while unpacking images, possibly some bug in firmware.
Received the X99Z V102 version. Never turned on after the build. Had to reboot dozens of time then it booted to Windows 10 on my SSD. Chipset is real X99/C612. Plugged in USB peripherals then it stopped booting again, not able to read the boot disk. RAM slot supports quad channel, paired with 2678 V3 and VRM is hot as hell. Made a tiny change on BIOS? Stopped booting again. Caused me too much headache, frustrated and got myself Z490 & i7 10700 instead. TL;DR: Unstable BIOS, weak VRM, stay away.