I have pretty deep insight into working with ruxit, as it's the company I'm with :-)
However, this is not the place I usually do business, so I'm not going to talk marketing here.
Compared to New Relic or AppDynamics one of the main differentiators is that it's pretty much ready-to-go. Install the monitoring agent and everything else is auto-detection, zero-conf or whatever you'd like to call it.
Compared to Nagios, it does all that - again - without any configuration necessary.
Concerning everything else, I suggest you just give it a try. Whether you like it or not probably pretty much depends on what you expect.
There's an extended free trial available, maybe that's the best way to find out.
Concerning your number of hosts, just contact us for a quote.
If you have any questions, please feel free to ask here or PM me.
Sorry again guys, I hope I was able to put my in an objective way.