I work in an agency that makes flashy marketing sites. My biggest concern with tools like this is always how it works responsively across viewports. I can make a change in dev tools and it can translate to my code, but it might not work at all when I drag the viewport up and down. Can you comment on how this product works on that problem?

If you make the page small and then make some changes, it knows you're doing so in a small breakpoint. So if you have mobile-specific styles and you edit some - these are going to remain mobile specific. I am working (right this second) on a canvas mode where you can see breakpoints side by side which will make this a bit easier than physically making your screen small.