These are my thoughts on the on premise installation since I have no experience with their cloud service. PRTG is a network monitoring application where your plan is to have simple monitoring using mainly SNMP and WMI, PRTG is easy to setup, easy to scale (if you plan for it) and easy to maintain. There are definitely some areas with custom sensors that could see some improvement, but if you put the time in (same thing with all monitoring tools probably) you can get most of your specific monitoring needs covered.

Paessler PRTG allows me to monitor the status of our network (including hardware) tools in real time, in a simple and efficient way. I use it daily to keep track of servers and network devices, which helps me to ensure our infrastructure is running smoothly and issues are detected early.