This is a kinder, gentler reply than the usual “why bother” or “its stupid” responses I’ve seen elsewhere
A lot of my riding is on country roads where you won’t see a car for 10-15 minutes, and I’m often riding into a strong headwind and can’t hear cars coming from behind. These are narrow country roads with no gutter and no shoulder.
After trying several different mirror systems, I settled on this “looks a little goofy” rear view handlebar mirror:
However in my experience is that relying on the mirror for awareness is hit or miss. So I was still getting surprised.
After reading about it on DCRainmaker, I bought the Varia 500 and planned to return it if not satisfied. Loved it, and honestly its just as useful riding in city traffic. I’ll never ride without my mirror and Varia radar. The Varia 500 has dim lights, so I have a Bontrager Flare RT rear light and using the Edge 520 light network feature the Varia LEDs are disabled and I just use the Flare RT to be seen. My new muscle memory in the city is to glance at head unit, check rear view mirror, and turn my head to visual confirm. So much better.
I said it earlier, after initial setup the Edge 520 and Bolt are more similar than different. For me, a couple of things tip the balance toward Edge 520 - I’d recommend the Plus version if purchasing now. Radar and light network support are two reasons. I can quickly take a TR workout and create an outdoor version on iPhone sync to Edge 520. After initial setup and one tweak, I don’t want to change the fields displayed so the Bolt’s ease-of-config is a don’t care. Strava routes have turn-by-turn - shape based on 520 and full routable on 520 plus. And full routable maps are handy if you want to re-route and there is no cellular data (or no phone).
IMHO if you just want something drop-dead easy to configure out-of-the-box via smartphone, then Wahoo is the answer. But if you have some patience on initial setup, then you are rewarded in the long run with Edge 520 plus.