EDIT. On second thought... The USP of Mender is that it's open-source and you can install it on-premise. I regret to say that currently the server install borders on unusable.
There is a "demo" install, it can work (I've seen it, it's nice) but it consumes huge resources, like 2 CPU cores and over 2GB or RAM, and it's more or less designed for a desktop machine. The qemu virtual device that comes with the demo (to receive OS updates) is a hog, but the server isn't lightweight either. (It's a bunch of Docker containers)
Then there is a "production" install, it should work in a headless server configuration but there I was simply unable to get it to work.
Besides that, the real problem seems to me the absence of "official" support, compounded by the absence of user community.
If the code has indeed any merit I wouldn't be surprised to see a fork.
So for now and for my part I'm getting stopped with Mender I think