Sorry this got missed, thanks for bumping it.
For end users, yes. If you do choose use it, tread carefully and review what those external repos are putting on the filesystem.
FlatPak is the supported/integrated solution by CL to get immediate access to a large variety of applications. In the mean time, the focus is to get more and more software packaged natively in CL as bundles.
To your order of methods for obtaining software, I would add “request the software to be packaged in CL” somewhere in there. If it makes sense and checks all the boxes for open source, it’s likely faster and easier for it to be included in the distro. You can open new package request on Github: https://github.com/clearlinux/distribution/issues/new/choose