IDFI is overall a good app to jolt ideas quickly in a couple of hours. The flow is right on: set up your walls, add doors and windows, add objects and play with your design in 3D. The app also includes a good quality renderer that creates great images that you can share or save to the photo library. You can even add floor to your project, which I think only IDFI can do, as far as I know.
Having said that, there are quite a few areas I'd like to see improved and rather quickly.
For a start, you can add floors but not stair cases, which doesn't make sense. You can't add a roof either...
Secondly, you cannot control the width or height of the walls, which I also miss a lot, in particular when designing high ceiling rooms over two floors for instance. So forget more complex designs with slanted roofs, rounded walls... But even at a global level, being able to set the ceiling height at floor level would be a plus.
Also, some controls could be more intuitive: as much as I appreciate the possibility to set objects sizes precisely using the dialog boxes, I'd love to be able to just drag handles the way it's done for rotating objects.
Finally, an export to Sketchup could prove invaluable, but now I'm probably exaggerating...
I warmly recommend this app and I hope that I'll get to add stars as new versions are rolled out.