I've purchased this kit and am absolutely delighted with it. I actually have open-outwards windows (contrary to the first reviewer) and I can vouch that the screen does indeed suit open-outwards windows too. It's simple to do this: the screen uses Velcro strips and so any edge of the screen can easily be unattached temporarily to access your window latch behind the screen. Open or close your window, then smooth the screen back into place. Very easy to do this.
Once in place, the mesh is so fine that it is practically invisible. The narrow strips of Velcro fix firmly to both wood and UPVC window frames and there is enough Velcro supplied to completely encircle the window. The mesh is easy to cut to shape (I recommend leaving a little excess for easier fitting).
The only difficulty I can envisage with open-outwards windows are the older-style wooden casement designs that use a metal horizontal bar to prop open the window. This bar will jut inwards through the mesh screen, and so you will need to allow slack in the mesh so that you can tuck it around this bar. More modern windows don't tend to use these prop bars and don't present this problem.