I used to buy mounts like that but they suck, seriously.

I hate the way the release button pops open, it feels cheap, it loudly rachets close, the holding arm block ports if you use a 770. I threw away the Akron ones I bought.

What I do highly recommend are the ones that look like this:
http://tinyurl.com/23f6ok
(not affiliated what so ever to this seller, I just randomly picked the closest pict)
The arms adjust for a wide or narrow grip independently. So you can have a wide grip for the bottom of your 770 to free up the ports, and more to the right to not get in the way of the buttons on top. It ratches close quietly, and opens with a smooth action rather than a jarring crack like in the Akron model. It also has a weird photo holder to put a pict when the mount is not holding your 770. Also it's has an optional vent mount for those of you who live in calif (window mounting is illegal).

You can find them all over ebay from various seller. I have one in each of my cars, and one in my bathroom mirror so I can listen to music while I shave.