It actually appears that their tracking can be used free in development mode without their server; it could probably be adapted to be used on a live site without their service as well.
I've used NewRelic quite a bit in the past, but only in production. I never really though of using it in dev. It would be good if there was a browser plugin or something to give immediate feedback about the most request that loaded the current page, as shown in the article.
https://github.com/newrelic/rpm