There is a discussion on the Openwrt forum about this GL-SFT1200 Opal and other less supported device and the conclusion by some of the outside developer is something like this:

There is a huge difference between a hacked-up and partially proprietary OS somehow based on OpenWrt on one hand and on the other having all the drivers needed and a recent Linux kernel built from source, having documented the code and it being accepted by the community after review.
The former is impossible to maintain in the long-run, meaning you will have to live with bugs and vulnerabilities because you can’t do anything about it (as not all components are available in source-code form – and even if we had those sources, I bet the code quality is so low that it would still need a huge amount of work to get it cleaned up and built on top of an up-to-date Linux Kernel).

GL-iNet has some interesting and cutting edge devices that is very affordable for the consumer, but with many of the devices the user must be cognizant of what can be expected of them and the limitations that one may have to live with.

This is a list of GL-iNet devices on the OpenWrt device page, the ones on the left panel are those that OpenWrt has device-pages dedicated to them and have a better chance of full OpenWrt compatibility.