Thank you Michael for your very positive feedback. For readers of your review I hope to explain: the black line is the 1.5mm thickness of each magnet which can only be seen when viewing the window at an angle. For many customers the sides of a window are covered by a curtain, or because the window is set within the thickness of the wall you can't easily look there. Customers generally look through the window during the day not at the frames, consequently their eyes are adapted to the brightness of the view outside. The line you mention is then hidden in dark shadow, as a result of contrast. In the evening most windows will be covered by drapes of some sort, so the panels are not visible then anyway.