The Stryd power meter packs quite a punch for a small device that clips onto your shoe. I have used it for about eight months now and have made the most significant gains in my personal running voyage. Training by power is really in its infancy, and not everyone has latched on, but the insights/metrics that come with Stryd can, without doubt, make you a better runner.
Heart rate is a lagging indicator that can be affected by stress, nutrition, weather conditions, and many other factors. While vastly superior to heartrate, pace also suffers when the terrain varies (hilly courses) or when the weather is hot, windy, or even cold. Power is constant throughout all those conditions as it is a measurement of what you are doing the exact moment you are doing it. Power can accurately assess the intensity of your workout, and that is where the gains are.
The Stryd power meter retails for $219, so it is a bit steep in price, but it is a great device that can truly make you a better runner. It works with all the prominent GPS watches. I can personally speak for Garmin, which requires you to use a CIQ field and an app like Run Power or Datarun and Coros, which works with Stryd natively.
"The power Duration Curve is your best effort power (in Watts) at any given duration (up to five hours) that you've done over the defined period of time" - Stryd
It takes a few runs to establish a baseline, and the more you run with it, the more in tune it becomes with your capabilities as a runner. To keep your Critical Power (CP/FTP) accurate, you must perform several essential max out sessions every 90 days, of varying times, so that it can paint a picture of what your capabilities are. This is known in Stryd as the Power Duration Curve.
Stryd offers training plans, and their PowerCenter platform gives you unique insights/metrics into your running. According to Stryd, this is likely to become a paid subscription model, but the cost and how it will all shake out are yet to be known.
One of the more unique features of Stryd is that you can input a course .gpx or .fit file and it will estimate, with great accuracy, what your finishing time will be if you maintain a specific wattage throughout your run. For instance, when I ran the Huntersville Half Marathon, the Stryd race calculator told me I would finish somewhere between 1:57:00 and 1:59:00 if I maintained an average of 310 watts throughout the run. I averaged 309 watts and came in at 1:59:22. The screen I used most during the race was my 3-second power and my average power throughout the race. I did peek at pace here and there to see if the device was indeed accurate, and it was spot on.
If you are interested in running with power checkout out the book “Run with Power” by Jim Vance and look into the google docs from Coach Steve Palladino, who trains his runners by power.