An unusual comparison at first glance, but bear with me. Now the 840 has 'all the buttons' it's a relevant question. So here's my answer
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Garmin Edge 840 Cycling GPS In-Depth Review
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Garmin Edge 840 Cycling GPS In-Depth Review
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Garmin Edge 840 Review
Garmin Edge 840, Compact GPS Cycling Computer with Touchscreen and Buttons, Targeted Adaptive Coaching, Advanced Navigation and More : Electronics