Thanks for the info, Robbie!
I've understood now that the core monitoring service Nagios is used on both editions!
I think chossing the right core component is very important in respect to performance of a soc like raspi. As long as you don't trigger many thousand ssh calls per hour, this seems to be irrelevant as well, since I bet, no one would choose a Raspi to monitor an airport to monitor 17.000 services. I hope so at least ;
My home has about 10hosts/200 services to be checked, it's perfect for that! Currently running 10% cpu with only 600mhz.
But, I tested both editions latest releases and in my opinion the learning curve is much steeper on check_mk omd, on the monitored client side there are pre-configured installations, that run right off the bat for any popular OS. On NEMSlinux you feel a bit left-alone, what packages you would need and what services you want to configure separately in the config file for the client, to make it even discoverable at all, you would have to search and config them, before you can use them.
If you are a hard-core old-time lover of nconf/nagios and the configuration of client-packages and configuration of their respecting config-files, then this is your deal maybe. If you are new to the linux-world, new to single-bord-computers, and new to the nagios-world, I bet you are going to have a hard time bringing this baby to hum in a decent range of time.
I like your setup procedure though, it's easy to integrate in your network, the SMTP relay and stuff. But I was already stumped on how to integrate hyper-v checks on my host, as a beginner you are clearly doomed to begin a journey through google. While that is not a problem, comparing this to the check_mk OMD, it's going to be up and running pretty fast compared to this experience.
I really appreciate your work that you did for the raspi community but as a beginner in this monitoring-world, the configuration of check_mk omd from the config-gui-perspective seems to be much more intuitive.
Keep up the good work, even though I cannot adopt it in a timely manner!
Cheers Don