I'm using one on a 2013 P2. Different bottom bracket. It works fine but I had to shim the whole power meter just a bit because the bolts were contacting the frame.

x2 I also had to use shims with my old P3C. I'd highly discourage buying a C1 power meter now as there are many better options. I could never get mine to stay working in the rain, but when it dried out, it came back to life and worked really well.

I have one on a Trek. The early versions of the C1s were susceptible to water damage. Mine failed and I got a warranty replacement. I think they mostly add a bunch of silicone to the gasket now and it does a better job of keeping out water. I love the meter! It's the most economical meter on the market (for two-legged power), is accurate and reliable. Mine pairs right up with Zwift, my Wahoo Elemnt Bolt and Cyclops Joule without issue. Zero outset is a breeze by way of iPhone app. Really the biggest drawback is the availability of the 5-arm spiders on cranks moving forward. I simple grabbed a 165mm 105 for dirt cheap and that's my 11-speed crankset (also works for 10).

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Madison photographer Timothy Hughes | Instagram

I just found on their webpage Q&A section, that it's not compatible with the cervelo BBright. bottom bracket.

well that stinks. I have stages PM currently but thought the C1 power meter might be an inexpensive option for dual sided measurement.

After my C1, I wound up buying a used SRM and could not be happier.

I've been very impressed with my C1. Works reliably and never gives bad readings. Live in a dry climate so water ingress hasn't been tested. Tested it extensively against powertap hub and trainer and is usually about 3.5% higher - consistent with drivetrain loss expectations. The price is ridiculously low for a reliable PM that works.

I'm a bit mystified about all the antipathy towards 5 bolt cranks. I have loads of different chainrings that I will swap out - have no intention of ever moving to 4 bolt. Lots of great 5 bolt cranksets out there going for low prices.

^^^^ This. Practically free.

I have been running a C1 for about two years now, no issues. I have mine set up on a SRAM S series crank with 5 bolt spider. This isn't on their compatibility list. However, it works with both GXP and BB30 cranks.

I have not experienced the water intrusion issues that others have had. Pretty meticulous about getting the o-ring just right before reinstalling the battery cover. Battery life is a little shorter than I would expect, but not overly short. If I compare it to my old Quarq it is certainly shorter and shorter than the battery life in a SL+ hub that I have for another bike.

Would I buy another one? Sure if the prices is right and I can find a crank I am happy with.

I suspect you may struggle for compatibility. On my wife's P2 I also needed to shim the bottom bracket 5mm to the right to give clearance for the chainring bolts on the chainstay. Because her P2 was the original it had a threaded bottom bracket so was easy to do - with a press fit life could be trickier.

Been using a C1 for three years now. It's been a rock. I'll buy another at some point.