Resizer: an interactive viewer for testing your responsive UI

They key here is that it's a shareable url.

That's much easier to send along to someone in product or a C*O who may not be comfortable with the dev tools.

I believe the audiences are different - the people who are using Resizer aren't necessarily comfortable in Dev Tools.

Also, since the resizing UI is drawn in the same window as the preview, it's usable on a tablet. If you're just doing a quick design review and are away from your laptop, this could be a good solution.

No https for the domain unfortunately, bookmarklet won't work on secure sites.

My immediate take-away was that this was some sort of stand-alone application or utility. After realizing it's a hosted service, the real benefit comes from being able to slug a URL and pass it along.

There is still a number of folks out there that might understand there is a mobile web, but might not necessarily grasp responsive design, or the variety of screen sizes and what they mean for a design... the initial UI on the resizer alone explains it pretty well.