I've had a play with it. Seems a little more intuitive then Adobe Reflow and definitely ahead of the other other ones on the market. I think in a few more releases it could be useful but you will still need some custom front-end development on top of it.
I'm looking to use it or Reflow to complete responsive wireframes. Currently on some projects I'm mocking up desktop / tablet / mobile and it can be quite tedious. I think a tool like this is also good for handing designs over to front-end devs. We outsource a lot of the front-end development and being able to give them a design that they can see at multiple breakpoints could be quite useful and save time overall.
Yeah I haven't really played with Edge reflow, Edge inspect is really awesome as a previewing tool though, brilliant for developing responsive sites.
I don't mind Macaw but it seems a bit weird not being able to see the code, everything is so abstracted from the DOM and their breakpoint integration is a little weird. I can't quite figure out who it's for, anyone who can code doesn't really need it, anyone who can't code would really struggle to understand it.