So Spigen promotes that you pair the mount with their thin case they sell (
http://www.amazon.com/gp/aw/d/B010M...sim_107_2?ie=UTF8&refRID=0Q32V08SKDCR6SQJCMXD - which I bought) that has a nifty indent for the metal plate to be inserted into.
Great case, nifty place for the plate. Big fan.
But I like classy cases, and the new saddle brown is pure sex.
The mount comes with a rectangular plate (the one I put inside my leather case) and an extra circular one that's a tad smaller but just as effective.
Anyway, the mount's magnet is strong as hell. I originally tried to use it with the incase smart (
https://www.incase.com/shop/iphone-cases/incase-smart-systm-for-iphone-6/blackslate/) and admit it was too thick, or the rubber on the inside was too much, and it weakened the magnetic attraction enough to dislodge the phone when I hit a medium sized bump in the road.
I tried going with the metal plate stuck to the outside of the incase case, but come on. What am I, a savage?
So I stuck it inside the Apple leather case, and it's strong enough that I made a trip from Maryland to Pennsylvania with no issues.
It takes a good amount of effort to pull it off the magnet.
tl;dr: Magnet is very strong, works in not-too-thick phones from the inside, almost too strong with direct metal to mount contact.
Mount is also on a comically good sale for $7:
http://www.amazon.com/gp/aw/d/B0109...igen+mount&dpPl=1&dpID=51SjtXv-FdL&ref=plSrch