So the main thing I see here is the high contrast screen. That looks a ton better than what's on the Garmin 500. I also like the LEDs on the edges.
If you don't need the navigation (I mostly ride the same n routes) do you think it is still a worthwhile upgrade?
We'll see how the screen performs in the daylight tomorrow. Indoors without a bright light around the screen looks fantastic. It's not as "pretty" as a color screen might look, but it's highly functional and easy to read. At the beginning of today's ride the room was brightly lit and I was having a little trouble seeing the numbers. With the backlight on it was easier to see, both with bright lights and in the dark. I've never had much trouble reading my Edge 500 in the sun outside, but I've heard that the 520 has glare issues. Maybe they changed the material or finish in the screen window?
I've grown to hate the user interface on my Edge 500 lately. I regularly ride two different bikes, each with their own crank-based power meter. Especially with the mostly-broken Enter button it's a huge pain to switch bikes on the 500. It's something crazy like 10 key presses to do the switch - hold Enter for 1.5s to access settings, arrow down 3 times to Settings, enter, enter on Bike Settings, arrow down once and enter, enter on Bike Details, enter on the bike dropdown menu, arrow to the other bike, enter, then hit back 5 times to return to the data screen! So that's actually 17 key presses! Unbelievably clunky interface. I'm sure they must have improved on that for the 510 and 520, but I haven't used those so I can't say how they are.
The ELEMNT interface is more elegantly thought-out. Granted, that's partly because most of the settings are on the phone app instead of on the device, but it works out well. Sensor acquisition is one of the few settings accessible from the device. Adding a sensor was a pretty impressive experience on the ELEMNT. I was doing it in a cycling studio with a room full of cyclists, each with their own power meters and heart rate straps. The device instructs you to hold it close to the sensor while it listens for a signal. I paired my power2max and my Garmin heart rate strap this way with two other riders within arm's reach of me, and the ELEMNT identified my sensor, and only my sensor. Compare that to the Edge 500 which I had to take 50 meters from the nearest bike before it would pair correctly, and I'm entirely satisfied with the improvement. The device also remembers multiple sensors not associated with a particular bike, so I'll be able add all three of my sensors (2x power meters, 1x heart rate strap) and switch bikes without much fuss. I don't yet know what happens when I have both of my power meters paired, turned on, and in range. Maybe I'll try that tomorrow morning.
Overall it's a joy to use the ELEMNT's interface, which is in stark contrast to the hassle of using the Edge 500. Of course there's a massive 6-year difference in release date between the two devices, so it's a rather unfair comparison. However if you have a 500 and wondering if it's worth purchasing an ELEMNT I'd say it's certainly worth it. No idea how the 500->ELEMNT upgrade compares to the 500->520 upgrade though, which is the real choice.