I have the 520 with the visual and unfortunately no audible alert. That wasnt good. Unless you just happen to be looking down. I bought the display unit later, but could not hear it at all. Typical of middle aged men. Our hearing isnt what it used to be. So I velcro it to my helmet over my ear. Still nothing, its just the wrong tone for a former fighter pilot. The gear is nearly useless without a Bluetooth connecting tone generator or a volume control. However, as someone using radar on every flight of my career, it works great to track vehicles. I Evan tracked a chasing dog once.
I bought the Varia setup when it was introduced. I ride 20 miles, 5 daysweek at 0500 on a two lane road with little or no shoulder. For me, this is mandatory equipment, it's bullet-proof. For rear lighting, I also run this httpsbit.ly2XynzFA
Part of my route is separate bicycle roads. The other is shared with cars. I was very skeptical at first to trust this device but Ive used it long enough and every single time it was dead on accurate. I feel naked without it now. I still turn my head to check but its good to know it has my back
I purchase these items to increase my safety margin and am extremely pleased. I did not want my 1030 display cluttered, which is mounted out front. The receiver display I have stem mounted. I am now never surprised, it only picks up closing traffic (even motorcycles) and makes crossing busy roads a snap. In a word- flawless.
For rural riding this radar is awesome, it picks up cars from a long distance. Paired with a Wahoo Bolt for me I have the Bolt LEDs set to warn me when a car pops up. It does an excellent job of telling you relative approach speed by varying beeps and colorspeed of flashing LEDs. And you can see one or more cars and their relative distance displayed on the edge of the screen in a strip like a road. Then I got one for my wife who rides a lot in my slipstream. She has the display for the radar instead of a device with a screen. I was surprised how tiny and light that display is. And in some ways it is better than a screen in very bright sun as the LEDs are high intensity. She was squeezed off the road by a guy passing into a blind corner and broke her pelvis last year. The radar now gives her a way to identify and manage approaching cars. Two negatives.... with the light on solid (it flashes when a car approaches fast) the battery goes about 4.5 hours. Another hour of battery life would be perfect. And in any sort of an urban setting the radar quickly becomes a nuisance, I just mute it. If you ride in an urban area dont even think about getting one, it will drive you nuts! But for rural use it is the bomb!! Currently using them on a long cycling trip in Australia and I am thrilled we have them with us.
I got just the main unit because I pared mine with a Garmin 820. Personally I would like that rear light on it to be brighter, but that is minor. The radar on it works flawlessly. It lets me know of cars approaching from the rear well in advance. I see the moving dots in the Varia Vision and hear the beep from the 820 (when used with a third party steering tube mount). All in all, it can greatly improve safety. Yes, when not on sale, it is expensive, especially when you need all parts (Varia, Garmin 820, and Varia Vision), but that is what it is and if you find the extra safety helpful, it is worth it (IMHO).
Thought this would be gimmicky but GPLama and DC Rainmaker gave great reviews. Ive found it to be very useful for telling the number of cars coming up behind as well as their speed. It is reasonably good (80-90%) with motorcycles and even some bicycles. it really is helpful in alerting you when to move over or when there is an opportunity to move to smoother road safely.