They were bought to stick the iPhone to random surfaces at home. So far I have put it on my nightstand, on my tower (PC) and in the kitchen.
The quality of the adhesive seems quite good without any peeling or slipping. If you somehow place it and put weight on the sticker until the adhesive stabilizes for another ten minutes, even better.
The magnetic strength is sufficient for a pro max mobile with an aramid case (heavy), so it is also sufficient for most uses.
For placement in a car, personally I would not recommend it as in Greece cars reach 45+ degrees in the interior and the adhesives may melt.
I will come back in the future if I notice anything.

Excellent magnet! For those who don't know what this is exactly, it is a self-adhesive magnet that should be placed on a clean and flat surface (you forget it if you have a curved dashboard). The adhesive it has is killer! The diameter of the ring is based on magsafe specs. I stuck the "ESR Halolock MagSafe Universal Magnetic Ring" on my phone case and these two magnetize perfectly and strongly. This specific self-adhesive magnet from Nillkin stuck on a Brodit Proclip (ordered from Amazon, separate for each car model). It has never moved since then and I have a OnePlus 10 Pro that weighs 205 grams together with the case and its ESR metal. The reason I resorted to such a custom mounting system is because (a) I prefer the original OnePlus car charger, as it charges it 100% in 1 hour and 15 minutes from completely off, while with magsafe wireless car charging it would take 3+ hours and (b) I wanted a mounting system compatible with any wireless charging. If you resort to simple magnetic mounting (regular metal adhesive on the phone and regular magnet attached to the car/proclip), you will have to remove the metal adhesive from the phone every time you want to use wireless charging. By doing the above, I can use wireless charging seamlessly at home and in the office while also having fast charging in the car along with magnetic mounting. Highly recommended!