I am now using my third Garmin Edge, I will say at this point that for a fair amount of money they are far from perfect, in fact all three models, 705, 800 and now 810 have all been replaced within 12 months under warranty and to me that represents a 100% failure record which I would class as woeful.
I do cycle most days so my Garmin gets used a lot more than most and I want to highlight a potential problem for all owners using the quarter turn mounts.
My 800 lost both of the tabs that retain it in its mount which I put down to vibration on the poorly maintained roads. After using the Garmin supplied mount I purchased a SRAM out front mount and despite a wasted call to Garmin who told me it was my fault for using a non Garmin product and there was no solution an internet search suggested this is a common problem and there is a solution.
A company from Newbury, Race Ware Direct http://www.racewaredirect.co supplied a printed tab repair that is fixed over the existing mount. After cleaning and removing the remnants of the old tabs with a file I used 5 minute epoxy resin to glue the new mount in place and I have taken the extra precaution of lining the bottom of the SRAM and Garmin mounts with a small rubber disc cut from an old inner tube to act as a shock absorber and eliminate any possibility of vibration which probably caused the failure in the first place.
A £10 repair that can save you the need to buy a new GPS device.