I believe the only difference between the two models is the latest version (515) is Bluetooth enabled allowing you to control the unit with your phone.

515 supposedly has slightly more battery capacity, and also a "Peloton Mode" (lower-lumen constant-on) for the light. Nothing about the 515 would make me pay more for it while the 510's are available at closeout discounts.

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"They're made of latex, not nitroglycerin"

Thanks. I saw the bundle for about $170 on Amazon. Probably gonna jump on that.

Do you have a Garmin/Wahoo head unit? If you do, you probably don't need the bundle.

DC RAINMAKER just compared the two and main difference is battery.
I just bought the 510 at 150 Euros when new one is 199 Euros.
I like to see if cars are coming behind, bery usefull for the weekend ride!
Great tool.

Ditto above... DCR's assessment was the only difference was Bluetooth. I have the 510, and I love the latest tech, but I am skipping the 515.

Also, I have the opposite opinion about Peloton mode. One of the fantastic features of the radar is that riders behind you can know of approaching traffic by your blink pattern. My fellow non-enabled riders love that feature. Peloton mode kind of kills it.

Sorry, I wasn't clear. The bundle is the front and rear lights. I already have a garmin head unit.

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.

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Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/

I've seen some great deals recently for the 510, but have keen interests for the 515 particularly for the bluetooth. I am often down on my aero bars without a view of my garmin computer, so audible alerts to my earbuds would be extremely valuable and increase safety. I realize that the computer will alert with tones on the 510, but I often don't hear it with my earbuds in.

Do you have a link to your "front page story?"

If you have Humana health insurance, sign up for their Go365 program. Using that, you can get at least 30% off Garmin products. The RTL515 is $130 through that discount program. The Garmin 530 is $195.

You can also sync your workouts to Go365 and earn Amazon gift cards, literally getting paid for your training. I’ve earned around $400 so far this year doing that.

One thing I would really like to see mentioned in reviews of lights is if they can operate while taking a charge. I found out the hard way after dark in rural Missouri that the Varia headlight cannot take a charge while operating (or be turned on while charging), but the Varia taillight can.

Love my 510 and the price new was great since the 515 came out. The charge is good only for one long ride or two to three shorter rides. I charge mine two to three times per week verses the once a week on m Garmin Edge 530. Longer battery life would be great.