I plan on doing something similar. I’m worried that putting another magnet on the back would mess with the charging, so I’m just sticking one of these on the back since the ball joint is the same size as the end of my Pitaka charger.
I use a similar magnetic mount, but attached to an adhesive mount that goes on the dash. In my jurisdiction, windshield mounts are not permitted, so the mount has to be below the line of the windshield, and I prefer it there anyway.