Garmin

This is one of those, 'didn't know how much I needed this,' purchases. The radar picks up cars further back than your ears can hear. I feel much more aware of what's behind me at all times. Can't imagine riding without it.

It works well with my Wahoo Bolt 2, though it doesn't remember my preferred flash settings (takes 15 seconds to configure pre-ride).

Battery life is fine. I can get several rides out of one charge if I'm only doing flash alerts. If I'm also using it as a persistent rear light it needs to be charged by the end of the ride.

Included seat post mount uses silicon bands to secure. Better clamp-based options out there.

I did a lot of research before buying a "fancy" bike computer. For years I had a simple bike computer that gave me cadence, speed, etc. But, with my new bike, I wanted something with GPS and routing capability. Garmin 840 does all that and a ton more. When it comes to devices, I've been trained to believe that either devices are ultra customizable or they work well. This device somehow manages to do both! It has a massive amount of capabilities and customizations and yet it works flawlessly. For example, it automatically found my SRAM AXS components, bike radar and uploads routes from my phone or computer quite seamlessly.

Highly recommend this

Between my wife and I, we have owned every version of the Garmin 800 series GPS. When my 810 died I bought an 830 for the front of our tandem bike. When we bought a second tandem for another location, we bought 2 more 830s for the front and rear because my wife, the stroker, also likes to have one. When her 820 died recently after many years we bought her an 840. This one is probably more capable than its predecessors but more complex to program due to the confusing menu system. Not to mention the 3 extra buttons. We don't use most of the available features; just navigate courses given to us on group rides. This unit has way more capabilities than we need, but it does what we need with a nice bright color touch screen and beeps that are louder than previous models, which makes them easier for old ears to hear.

I had an Edge 530 for several years before getting this, and I loved it. Upgraded to the 840 because it was a good price and waiting to spend $200+ more on the 850 didn't seem worth it. This is definitely a good bike computer--it does everything you could ever want and lots of things you'll never want, or even be aware it can do. That said, I knocked a star compared to the simplicity of the 530 because this thing is beeping at me and throwing up ClimbPro screens constantly, and it had a run where it wouldn't wake up without me hard restarting it several times (that seems to have gone away for now). You can change the settings to make it beep less and turn off ClimbPro, yes, but it's so excessive out of the box that I have to point it out. And I liked ClimbPro a lot on the 530, but this thing considers EVERYTHING a climb. Literally, any incline it seems. I actually got lost on a long ride because the computer kept throwing up ClimbPro and the new hazard pop-ups over my navigation as I was going 20+ mph and I had to stop, figure out how to exit back to my nav, turn around, try to figure out where I was going in advance (because when I went back the screen popped back up again), etc. If you can't tell, it got in my head a little. BUT, with all that behind me, this thing is a darn good computer.