What the picture on the box isn't showing you is that the iPhone itself won't stick to a magnet, so you have to attach a piece of steel to the back of the phone with double-sided sticky tape.
I would be more worried how it would affect the RF signals on call. If putting on certain cases can affect call quality as it would block the signals, why can't magnets direct attachments interfere?
I’ve been using this now over a month and love it! So nice to not have to clip it in using the stupid spring arms and/or ruining my air vents with the stupid clips.