I have been using devices from GL-Inet for many years and have had experience with a wide variety of devices from this company. (ar-150, ar-300, ar-750, sft1200-opal and others).
Basically, I was always very satisfied with their devices. I came across GL-Inet while looking for routers that can be operated with OpenWRT. Before I had made a few bad purchases, e.g. TP Link routers that were announced as revision XX and were then delivered as revision XY, which was not compatible with OpenWRT and could not be flashed.
In principle, it has been the case for years that the router call ends up in a self-built GL-INET interface. The front end comes from the GL-Inet repository and consists of a number of packages that can be de/installed with opgk. For a number of devices, e.g. the ar-750 series, pure OpenWRT versions can also be downloaded and installed from their website. They then have luci installed and you end up directly in OpenWRT when you call up the device.
Personally, I didn't think that their own interface was that bad at all. GL-INET concentrated on the really important things in router operation. And tried to make it as easy as possible for less ambitious users to put an OpenWRT-based router into operation.
They even have more complicated things like an OpenVPN server displayed in their interface. Simple OpenVPN connection scenarios can be mapped with a few mouse clicks. In the newer versions they have this built in for wireguard as well.
Completely sufficient for simple scenarios, but as soon as you need something else, e.g. a network network coupling, their solution cannot be used. They use completely non-transparent solutions for these things and generate, for example, firewall rules and binaries calls on the fly and completely ignore the way these things are solved in OpenWRT. That's why I've only ever used the luci interface and implemented things conform to OpenWRT.
The informations presented here in this thread were absolutely not clear to me and I believed until yesterday that these are devices that follow the ideas of the OpenWRT community.
But I was surprised that, after updating to the latest version of the software on my SFT1200 (which is a good, reliable router with a verg good price-performance ratio), OpenWrt 18.06 r0-d5ed025 is still shown as the base system, although GL-INET itself specifies OpenWRT 19 as the base in their release notes.
However, after reading this thread here, I now understand this and see that https://github.com/gl-inet/openwrt/tree/openwrt-18.06-siflower is just a branch of her own fork in which they integrated the siflower SDK. But probably not even manage to do that for OpenWRT 19.
This is of course an extreme disappointment. And unfortunately I fell for the grandiose statements on their website. Awkward!
greetz
Klaus