I am using it for my web development project which is about creating websites with responsive design in mind so that they look good no matter where or how much of screen size there are available (from desktop computers all way down through tablets).
It's really easy as well! The only thing i dislike sometimes when working online at work because most people don't have this software installed but if its not an issue then thats great!! Sometimes we need something like modernizer toolbox just incase our page doesn;t render correctly without them even though everything looks fine otherwise - maybe some users will see blank white areas instead? Maybe another option could be having both options side by each other rather than replacing one feature/browser compatibility test from your current code base?? Just thinking out loud here since im still learning these tools :D But overall very nice website testing library especially considering their free plan offers up enough tests already while also allowing us flexibility over certain things such as javascript enabled vs disabled etc.