This is a relatively cheap rebranded gigabit router (Rosewill Dual Band Wireless AC750 Gigabit 802.11 b/g/n up to 433 Mbps, 5.0GHz Wi-Fi Router RNX-AC750RT) which unofficially works with the OpenWrt firmware.
By taking out the two screws from the bottom of the router you'll be able to pry the plastic shell apart to access the inside, which reveals that this is just a rebranded TP-Link Archer C2.
From my tests so far, the Archer C2 build from a community thread seems to work great - even the 5GHz/2.4GHz WiFi. You can find the steps to install OpenWrt below.
Make sure to compare your router to the images first! Supposedly there are different versions of this router.