The illustration shows two 'prongs' that I assume slide between the slats in the vent, but how is it secured?
I forgot how they came from the factory but I believe they have a socket where the ball from the 520 is pusher in. Look at your 520 manual to see which way the device must be held to remove/insert the ball from the magnetic holder socket. Do not take apart on a daily basis.
I had a 600 which is quite a bit heavier than your 520 and had problems holding it tight to the dashboard. The problem comes if the vent slats are relatively thin. As you can see from the picture below, when the tips are tight there is quite an air gap at the heel of the mount.
I tested pre production models and recommended not to have radius in the back as all cars have different dashes.
The fingers seen are tightened by rotating the grip, same as with the current suction devices.
Push the fingers all the way for ward then rotate the grip to clamp.
If the slat is relatively thin the tips will clamp but with bumps on the road the device has a tendency to wiggle left right, but not fall off. If it wiggles, the tips are so tight that the holder cannot be pushed forward without first loosening the rotary lock.
If it is like that, either but some resilient material on the fingers or put a piece of foam on the sides of the curved back.
In spite of the above, quite a few people like using it.
You may not need it with the redesigned magnetic mounts of the 520/620 but on my 600 I had to hold the bracket with one hand while removing the device.
If the above does not apply to you, take a picture of your mount and attach it with your reply.
