Three months ago I’ve started using Skylight as app monitor and profiler, and I’m very happy with it. Skylight relies on running an agent that collects performance information from Rails app. Skylight has a minimal and simple interface. In my experience having a large and overwhelming amount of information and metrics can be disorienting. Tools like New Relic come with a lot of features and graphs, but someimes you can’t find the right information in the right place.
I definitely suggest trying Skylight out to profile your application.
You can try Skylight for free on Heroku. The installation is super simple and the installation screen provides real-time feedback during gem installation and configuration.