We released the Hype Reflect update a while ago, but hid the responsive design feature until 3.5 was available. The new feature is at the bottom of this page: http://tumult.com/hype/reflect/, which we call Responsive Preview Mode.
It was hidden in Hype Reflect before Safari’s Responsive Design mode hit Safari 9. I feel like they work very well together. Give it a go and let us know what you think!