Using it on all of our services, we all love it. Troubleshooting and optimizations are ridiculously simply, there isn't much investigation, APM just tells you what is wrong, saves a lot of Dev time and we'll worth the money IMO
What language? I tried Python Django a year ago and didn't get half the detail NewRelic shows out of the box. Given the much higher price I didn't even bother looking into custom instrumentalization.
But a year has passed, maybe I should give it another try since NewRelic is trying to make everything as hard as possible with their new UI.
Just to add, I love how easy it is to set up and roll out.