If you are thinking about it, get it.
This is one of the very few "must haves" on my list of equipment. Most of my riding is either on trails converted from former railroad grades with lots of street crossings, or country roads. It is difficult to convey what a difference it makes having complete awareness of when another cyclist or a motor vehicle is approaching from behind and going to overtake you. You can easily tell the difference by the speed at which they are approaching, and if it is a big mass coming on fast, the red alert side bars get your attention.
There are three things that take some getting used to. One is that you cannot really control the Varia radar unit from the edge device. What you do, is press the Varia's on button until it is in the mode you want, which is obvious from its behavior, and which is also displayed on the Edge computer if you go to the right screen. But, you can't change the Varia's modes from there.
The second caution is that connecting it to a supplemental battery pack via a micro USB cable only works if the cable is a charge-only type. The mere presence of the copper wires for comlinks in a regular micro USB cable is enough to cause a problem, even though they aren't talking to anything. It's enough to cause it to disconnect from the Edge and go into charge-only mode.
The other thing to be aware of is that the mounts for it are very limited. They work for directly mounting to a seat post, or to a bag with a clip strap that anticipates the need such as most under seat took kit bags, and the heavier panier racks with a full width mounting bar across the back. Not easily supported are the older Blackburn racks with a single center hole mount, or the high end Topeak carbon fiber beam racks from Japan that mound directly to a seat post. You will have to make some custom mounting solutions for both of those. I got the lower cost Tusita "Out Front" mount and cut it to adapt to the reflector mount on my Topeak carbon fiber rack, and it works perfectly.
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