I've been using this almost every day for about a month now. Phone GPS facing me, phone flashlight facing forward at night.
The arm twists and rotates to what I would imagine would be appropriate for any rider and bike, and can hold the phone vertically or horizontally.
I've demonstrated to others that giving the phone a solid whack at just the right angle will indeed eject the phone, but in practice the worst potholes haven't been able to budge it. I have noticed that with the size of my particular phone model, a good squeeze of the side arms will get an extra click from the locking mechanism and hold it tighter.