Which QGC version / branch / tag should I currently use?

I know that the modified QGC source intended to be installed on the Herelink is found at: https://github.com/CubePilot/qgroundcontrol-herelink

… But which branch / tag should be used?!

One might assume that the head of the master branch is the “current stable release”. In this case, that aligns with the v3.5.5 tag. That version of QGC is quite old, however. Compared to the current QGC mainline (which is currently on v4.2), there are radical divergences in the source, the UI, and the build dependencies / configurations.

I see that there is a v4.0.8 branch / tag on that GitHub repo. Reviewing the history, that code is completely disconnected from the revisions CubePilot added to create the 3.5.5 Herelink release. Instead, the customizations were started over from a newer QGC base.

I would expect that if v4.0.8 is the “current stable release”, that it would be on the master branch (per Git Flow standards…). Seeing it NOT be leads me to wonder if it is either a) and WIP or b) intended for new / different hardware?

I have a Herelink with the v3.5.5 build on it. If I install the v4.0.8 build, is there any reason to be concerned with compatibility? Does the whole OS image have to be reflashed onto the controller for that app update to be fully functional/stable?