The updated web interface in PRTG Software Maintenance 8.1 is much faster. Also, Paessler provides a sensor that gathers more complete information. This is a great feature, whenever the server running PRTG is rebooted, there's a short window where data is not gathered. With an additional installation of PRTG running on another server, the data gathering will not be interrupted. With this licensing model, you can run up to 5 instances as a cluster.