Perfecto - stable, easy, and convenient.
I received mine yesterday. I love it! The previous mounts I've tried were the typical cradle suspended with a suction cup. One thing I've learned is that suction cups die within 6 months, and cradles are a pain in the butt to use; they are sometimes impossible to use with one hand. This thing, after you slide the magnetic plate between your case and your phone, with one hand you can hang your phone up and take it down. The magnet itself seems plenty strong. I'm not worried that my phone will go flying during hard cornering or a bump.
The product itself seems well constructed and sturdy. My only quibble is that I was nervous about trying to get it onto the vent fins, as they are not heavy plastic. The rubber fins of this mount are quite stiff. I probably will not be taking this on and off much of the vent, as that would increase the chance of breaking the vent...
All in all, I'd highly recommend!