This kind of makes sense. Old one for the older versions, new for the newer. However, apart from how to install it, there's no documentation about the newer extension. I'm presuming that the built-in nx* functions are all there, but given the lack of documentation I can find, I don't know if it's all the same or not.
Yeah, you've kind of caught them at a time of transition.
The older model – which is open-source, so you can actually see all the available resources – was made by the Unix Services team and is written in an unholy mix of C and Bash scripts. And other stuff. The newer model is coming from the PowerShell team, mainly, but it's a work-in-progress as yet. So I don't know of any documentation, but the generic DSC documentation should work, and on a Linux machine where it's installed you can run Get-DscResource to see what resources are installed. Basically everything in The DSC Book is applicable.
Sorry for the late reply, but thanks for the input. I finally managed to figure it out and find out that the documentation was incorrect. The "EXCEPT 12.04 LTS, 14.04 LTS, 16.04 LTS" should have said only supports those.