The question is if the magnet will really destroy the quality of a camera?
The iPhone's camera uses optical image stabilization (OIS) and closed-loop autofocus (AF), which rely on magnetic sensors to function properly.
According to this article: Magnetic accessories might interfere with iPhone cameras - Apple Support;
"If you place a magnet near these sensors, the magnetic field will interfere with or temporarily disable the sensors. This can degrade the sensors' accuracy and limit the range of movement available to the lenses. The camera will continue to take photos with other means of stabilization but without the benefit of OIS and closed-loop AF."
The article also mentions how to avoid magnetic interference.