Simple and clean, well done. The tilt options are a nice touch.

A few suggestions:

- Add example(s) on the home page. This is the first thing I look for, it took me a few seconds before I noticed "Try a demo image".

- In the case of a mobile screenshot, if the image is horizontal then the camera location on the "fake" phone should be moved to the side. Currently the camera remains on top, making the phone look more like a laptop screen.

- Add a button to reset the value for each individual property (size, space, tilt...etc).

- For some reason when switching from "Browser" to "Mobile" mockups the canvas shrinks to a small size. I'm using Chrome.