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
Garmin Edge 840 vs 530: Is Now The Time To Upgrade To Touchscreen? - Sportive Cyclist
Garmin announces the Edge 540 & 840 series of cycling computers
Garmin offers more solar charging with new Edge 540 and Edge 840 Series GPS cycling computers
Garmin Edge 840 Cycling GPS In-Depth Review
Garmin Edge 540 & 840 Compared: IN JUST 6 MINUTES!
Garmin Edge® 530 Bike Computer with Performance Insights
Garmin Edge 840 Cycling GPS In-Depth Review
Garmin Edge 840 Series In-Depth Review: 21+ Things To Know!
Garmin Edge 840 Cycling GPS In-Depth Review
Garmin announces the Edge 540 & 840 series of cycling computers
Garmin Edge 840 Cycling GPS In-Depth Review
Bike Computers and Technology Archives - Sportive Cyclist
new Garmin Edge 540 / 840 - ClimbPro bugs galore
new Garmin Edge 540 / 840 - ClimbPro bugs galore