OpenWRT underlying version is independent of the device. For example. my Marble has OpenWRT 19.07, but firmware version is 4.5. OpenWRT version depends of the chipset manufacturer mostly. I don't know if my Marble's OpenWRT will be updated with 4.7. But, whatever OpenWRT version has underlying, I only want that it performs well.
The version of OpenWRT you link is the fully open version. GL.Inet firmware is based on OpenWRT, but versions of it varies by device. But features are the same on all devices except when advertised.