I've spent the last 8 weeks working on "Test profiles" (The launch post is here: https://medium.com/get-calibre/announcing-test-profiles-and-...) — It allows you to emulate hardware devices (cpu speed, user-agents and screen dimensions), as well as limit the bandwidth (latency, download and upload speeds), and set cookies (you could use this to log into your app, test a staff-shipped feature, or maybe turn off advertising and see the performance impact.) I think I've finally got the basis of a really powerful tool, and I'm keen to share it with… everyone! I do everything myself, so if you've any questions, I'm here to answer them!