I've got the new Varia models in hand for testing right now, and largely I think the above comments are on target; most folks simply won't see any difference between the models.
That said, battery life of the 515
is better, but I thought the battery life of the 510 was already really good. This just means It will take longer for me to forget to charge the thing before a long ride :)
Ditto above comments on "peloton mode". I think seeing the flash pattern change on a varia equipped bike in the group is a plus, and haven't ever had anyone complain about my blinky on a ride.
Blue Tooth capability might be a real plus for some people, though. A fair number of people asked about ways to pipe Varia alerts into headphones, or increase the volume of the alerts, and doing this with your phone might be a good solution. I just started testing the new units, and haven't gotten to this yet, but stay tuned for a front page story in near future.
Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
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