I'm only doing this because I am really familiar with their node.js implementation, and even then, I'm still rather lost.
@bentael Unless you are running on an SSL forum, there is no way to iframe their interface without "warning messages". At least, that was the case last time I tried (last year or so). I'll do some research into it and will include an iFrame if they allow it.
@BarveyHirdman Currently, there is one limitation, being that you have to manually map the location of the newrelic.js file to the nodebb-plugin-newrelic location. I'm trying to see if I can ship a modified version of New Relic node.js implementation with this, but it has a proprietary license. I'll contact them to see if I can do what I need.
@planner Graylog2 seems very interesting. However, New Relic is an external service and can measure things such as speed more accurately, not to mention that you don't have to host it (my reasons to use it anyway). I will keep an eye on Graylog2, though.