I put over 150 miles on the Garmin RVR315 over four separate rides for a fair evaluation. The device certainly adds another layer of safety and keeps you aware of approaching traffic from the rear, for the most part...I'll explain in a moment. It integrates well with my bike GPS (Hammerhead Karoo) providing visual and audible warnings via bluetooth. It is most effective in rural areas and can single out a car very nicely. It urban areas, there are so many cars that you get overwhelmed with alerts, so not as useful in differentiating one car from the next. There are just too many audible alerts to make sense of what is approaching. The main problem with the Varia is that quite often there will be a visual warning (yellow status) on my bike GPS WITHOUT being accompanied by an audible alert!! Sometimes there is no audible alert at all!! Other times, there is only an audible alert after the car passes and alert status goes to green...what good it that? I may have a defective device and plan on returning it for a replacement. I'll update this review after I test out the replacement. In conclusion, when Varia works properly it alerts you simultaneously with an audible tone AND a visual alert simultaneously, and it gives you the opportunity to manage the road better and for enhanced safety. But, I don't trust it's inconsistent performance. Without an audible tone accompanying the visual alert, what good is it? Even if it did work perfectly, there is no substitute for the good old helmet mirror. But, together they make a good team.