To answer my own question.. there are two holder styles by ProClip, one that you adjust to allow the phone to slide in and out and grabs the phone by the sides (w/ or w/o charging dock - [demo video]) ... and another that is non-adjustable and grabs the phone top-to-bottom via spring-loaded clip (w/ charging dock - [demo video]).
So new question: Which type is better?
Mines not adjustable, it hold the phone by the sides, the phone snugly slides in from the top, no spring loaded clip.