I'm excited to try out the Sram S975/Quarq Cinqo Saturn power meter I just installed on my training bike.
If you're not familar with power meters, read the following. A power meter a device that measures the amount of power (work per unit of time) a rider puts out on the bike. Power is the best way to measure performance because it's independent of the environment or the riders physical condition.
Speed might vary because of wind, hills, road conditions, or tire pressure. Heart rate might vary because of illness, dehydration, or stress. Any of these factors makes it difficult the compare workouts from day to day, week to week, or year to year. Power measurements are much more standard since the measurement is independent of these factors, so you can compare any power measurement from one workout to any other. This doesn't mean that a rider's power output won't go down when he/she is fatigued or sick, but the measurement is independent of whether he/she is tired or sick. Whereas, heart rate could be higher or lower because of physical condition despite the level physical output.
The installation was super easy, partly because I previous had Sram crank set on my bike. All I needed was a 8mm allen wrench and a bottom bracket wrench. The drive side bottom bracket cup needs to be removed to install a cadence magnet/washer between the frame and bottom bracket cup. The installation took 5 min. If you weren't previously using Sram, you would probably need to install a Sram bottom bracket. If the pictures aren't clear, the Sram S975/Quarq Cinqo Saturn power meter is a crank set application. There are other power meters that are in bottom brackets and hubs. The upside of a crank set power meter is that the user can switch wheels on the bike (training wheels or race wheels) and still get power readings.
Since the power meter is in the crank set, use either a Garmin head or add on a ANT+ speed sensor to get speed and distance measurements on a Joule head. The battery life is about 500 hrs or about 10,000 miles @ 20mph, so I expect it to be a reliable, durable, and low maintenance setup I can ride everyday rain or shine.