Hi,
I second all these points, and would like to add some more:
I don't know any other solution where I'm able to rollout the client agent without root rights. We created a script to rollout and configure the base Xymon agent without any root access (only the user must be there), including a cronjob to check and start the client, inserting the ssh keys and so on. No /etc/init.d entry or so. 30 seconds job.
Even our DMZ hosted clients work over a ssh tunnel and port forwarding via ssh port 22. No extra hole in firewall, no entry in /etc/services.
And one more point: I would never trust a monitoring solution where I cannot see an only demo. Sometimes I can find some nice screenshots, but never this kind of live system view like xymon.com!
such a great product with a great community
Norbert