This is a very useful tool to have at so many levels. One reviewer wrote that the lack of extensions is terrible. I disagree. You can still use chrome if you need specific extensions.
With what is has out of the box, Sizzy is excellent. Well made, well thought out, polished. It's a gem.I use it not only for responsive testing and coding-related tasks (it allowed me to find a nasty bug that escaped us for quite a time); but I also use it for other stuff such as dealing with various accounts (such as gmail) and splitting views of the same app on one screen.It's similar to the way I work with Nova on MacOS. The possibility to use different user sessions is cool. I really like the philosophy : qr code for local testing on real mobile, URL editor with parameters, page navigator, a useful style inspector, an API inspector and so on. This is absolutely one of the best products I have ever bought on AppSumo and a no brainer at this price point.