you can use master or any other branch, but without warranty.
The usual approach (and the one favoured by GitHub) is: features are developed in branches. When they are considered stable enough they are integrated into the master (pull request). Hence the master is kind of "latest greatest", but with a certain risk of being spoiled. There are also forks from other user with their own masters and branches. Don't confuse them with the ones from the KLayout project.
But eventually, when the master is considered to have a sufficient quality, a release is made by creating a release tag (https://github.com/KLayout/klayout/releases). A release is a snapshot which is then turned into Windows binaries, Linux packages, PyPI wheels etc. This this is a lengthy process and I don't want to do this too often.
I'm looking to pull down a "latest, greatest" release and I'm still a bit confused between github, klayout.de various source bundles that all seem to be called 0.26. Is one of them better (newest yet vetted as stable-enough) than the others? Am I right to assume that the klayout site downloads offerings are the best to use, if I'm not going to touch the code myself (I'm not)?
Mainly keen to look at the present behavior of bindkeys redefinition, and also want to be working with the best version of DVB - looks like DVB latest is July timeframe, maybe has stabilized?
Also, re foundry PDKs and NDAs and such - I could ask them about support for open source based PDKs, and what info in what form I could provide somebody who can't execute one (I'd like to understand why you feel you can't).
My personal goal is to create multiple klayout PDKs but I'm seeing that my verification scripting abilities are not up to the task.