They are a bit thinner than the brand I used on my previous phone but are still held in place with a magnet, no problem. And I weigh a Note 9 with a round rim and don't have any shifting/rotation issues due to the weight. I bought a cheap case to use in the car and the disc is on the outside so can't comment on how well they hold up with the case in front of the magnet. I don't want metal touching the back of my phone, even with a screen protector. Note: I'm pretty sure the adhesive doesn't differ from one manufacturer to another and my last one survived the Minnesota winter and summer with no problems. So a pack of four should be more than enough.
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