I've done at least 400 rides since I got my 705 in the fall of 2010, and the mount is still good. Even the little tab sticking up that locks the 705 on the mount looks like new. I remove it on almost every ride, and often took it off again when I put the bike on my old bike rack.

I only have to use very light pressure and push the release lever down about a millimeter to release the Garmin. I put a little sideways force on the 705 and I can feel when the tab releases.

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My mount looks like the one Looigi posted:


It has a textured surface, not smooth like your photos. The base of the tab arm has no discolored, warped look like plastic gets when it's about to break off. Maybe they've changed the mounts in the last few years?