I like its scalability thanks to slaves. You can add as many slave as you want, which also allows you to reach and monitor devices running on the network that are not accessible by the master. It also has good roles management which is very useful for a service provided to customers. Lastly, it also has a nice GUI.
Improvements to My Organization:
Before we used Nagios. It's based on Nagios too, but the biggest benefit when compared to it is the simplicity to set up and modify devices.
Room for Improvement:
SNMP traps management to be improved. It's not so easy to use and you have to pay more to get the SMS module.
Use of Solution:
I've been using it for 30 months.
We have had no issues with the deployment.
There have been no performance issues.
It's been able to scale for our needs.
We used Nagios previously, and it was reliable but hard to configure, and even harder to create a master/slave configuration.
Considering the complexity of our network, it wasn't hard to install. It would be preferable if you have some Linux knowledge prior to the implementation.
We implemented it in-house via our Data Center Team.
Cost and Licensing Advice:
As a CSP, we have an MSP agreement so that we can pay for its use. It means that additional customers will pay additional fees, and this is invaluable.
Get a good book so you can get exposed to all the great functionality in PostgreSQL. I would highly recommend looking at the postgresql.conf configuration settings when you are ready to go into production. In order to get a good price, I think that you need to have a commercial process in place.
Disclosure: I am a real user, and this review is based on my own experience and opinions.
May 30 2016