I bought a pair off the Mothership a few months ago. Cheap, solid, does what it says on the box. I use it with a Samsung Galaxy S7, no issues. Do a test fit before you put the adhesive on, make sure there’s going to be enough space for your phone.
An update to my own post. Yesterday mine stopped working. There is a rubberized piece that is glued around the magnets to stop your item from slipping off. the adhesive has come loose and my phone hit the floor with a thud. All is OK, it’s got an Otterbox on it. 
Now I’m trying to decide if I wanna be cheap and try to glue this back on, or use my backup mount.
Agreed. The magnetic sticker that attaches to my phone will hold for about an hour and then the phone drops to the desk. Not sure I want to do the Gorilla Glue thing just yet.
I tried gluing it back on. The glue holds the rubber on well, but now apparently I’m not getting enough magnetic adhesion, my phone will sit for an hour or two but then without warning falls off. I think I need another solution.
On the off chance any of you are mildly functionally-challenged like myself 
…
Make sure you remove the spare steel circle from the magnet on the mounting bracket, otherwise, you won’t get a solid grip and your phone will keep sliding off. 
You’re welcome. 
For things like this, a cheap/tiny neodymium magnet does wonders. Just replace the provided craptastic one with a super-glued decent one.
Don’t use any adhesive/bonding solution that heats as that may affect magnetism depending on the Curie temp of the materials used. Using a lot of physical force can demagnetize as well.
Everything included but the magnet is really the money here… let’s be honest lol that looks like an afterthought of a magnetic solution from the pics.