I have run both the OpenWrt 19.07.6 released code and some of the snapshot builds for the upcoming OpenWrt 21.xx code (real bleeding edge stuff) on different GL iNet routers. The OpenWrt GUI LUCI has a steep learning curve, but if you want to do something special with your GL iNet hardware, like adding a second long range external WIFI radio using a USB adapter, it is the only way I have found to do it. The OpenWrt firmware is much smaller then the GL iNet firmware, as you only install the packages you are using. With the OpenWrt firmware you can target the firmware to the problem you are trying to solve. This gives your router a smaller attack vector, as there are less packages installed that may have security issues.
I have about a half dozen different GL iNet routers, doing all different functions for myself and family. Depending on the function, I am either running the GL iNet 3.105 firmware with work-arounds for the dnsmasq bug, or OpenWrt 19.07.6. It is much easier to setup the GL iNet GUI to configure things, as long as you don’t need to play outside the box, and you are willing to work around known bugs. This means reading this forum religiously, as it is the only way to find out about new bugs.
If you want to have the most control and the quickest access to patches for security bugs, go with OpenWrt. It is not that hard to do a simple setup of a GL iNet router with OpenWrt and LUCI. There are several youtube videos showing how to do the initial setup. I have used the GL iNet firmware update page to load the OpenWrt firmware, and I have used the OpenWrt update tool to re-install GL iNet firmware, without having to use uboot. It may not be recommended, but it works and lets me test out both sets of firmware. Try OpenWrt and see how you like it! You can always go back.
If I am using the GL iNet router as a travel router, where I may need to change a bunch of stuff to get it to work with some hotel WIFI, captive login and firewall, I normally use the GL iNet firmware, as its faster to make these changes on the fly, and to reconfigure the VPN client. If I need to do anything special, outside of what the GI iNet team documents, I use the OpenWrt firmware.