I recently bought some of the stick on magnetic button type phone mounts on ebay, the base magnets have good with adhesive but the steel discs that you stick on the phone had are junk, they would not stick properly on my lifeproof case, the power of the base magnet pulls them straight off. Not a total loss though as they where very cheap and base magnets are fine and will come in handy.
Thought I would bite the bullet and buy some Scosche or aerpro replacement discs that you stick on you phone or case, the Scosche are normally $19 at hardly normal and JBhifi.
I went into a Repco and they on sale for a three pack of different sizes, way better adhesive they stuck on fine don't know for how long though.
The catalog sale link does not show the the actual item, just another mount on sale.
Here is the link to the plates on the scosche website
mine from aliexpress are 3M adhesive and never fall off the case. If they ever did, i'd just use super glue to put in back on the fone case.