The Wahoo Fitness dongle turns your iPhone into a full-fledged, GPS-enabled ANT+ power meter head unit.
Want a great head unit for your power meter? Well, guess what? There's an app for that. Or, more accurately, there's an app and an accessory. The iPhone doesn't have the ability to communicate over the ANT+ protocol, so Wahoo Fitness has developed a product line based around giving it that ability. There's the hardware, which you plug in to the iPhone's dock port, and a free app to go with it (search for "Wahoo Fitness" in the app store).
It doesn't really matter which of Wahoo's several ANT+ attachments you buy, they will all work the same. The only difference is how much bulk and how much weather protection they will provide to your phone. For indoor trainer workouts, I almost exclusively used the Fisica key. It's a tiny little dongle that just plugs into the port. I put the phone on a little table next to my bike, put my headphones in for some tunage, and just grind away. For outdoor rides, I'm using the Bike Case, epoxied onto my Speedfil A2 creating an unholy Frankenbottle that perfectly fills the gap between my arms, and keeps my data right in front of me.
My Frankenbottle - Speedfil A2, custom straw setup, and the Wahoo Bike Case.
The app is great. It paired very quickly and easily with my Quarq, and I was up and running in about two minutes, after putting in my data and TrainingPeaks account info. The app keeps your screen from going to sleep, so your data is always visible during the ride. It isn't an adjustable display, but that's of little concern, because the app makes excellent use of the iPhone's large screen real estate to show you a ton of data at once. There are four screens in total, that will show you every metric imaginable (including some of the more esoteric power metrics developed by the authors of The Book). Yeah, it would be ideal if there were adjustable displays, and hopefully they put that in the future update. But hey, the app was free, and I'm not complaining. Their app is great, but they're the first ones to tell you that there are plenty of others that will work with their ANT+ Key. And another great feature of the software is that it uploads directly to TrainingPeaks for you (more on TP later in the Power Up series.
The Frankenbottle nicely fills the gap between my arms, keeps the water at the ready, and keeps the data always visible.
Of course, like any software, there are some drawbacks. Uploading to TrainingPeaks takes five taps (Pause, End, Save, Share, TrainingPeaks). It'd be great if that upload was automatic. And I don't want to get to the end of a three-hour workout and accidently hit Discard instead of Save. That would be a sad day - saving should be automatic as well. There are also a couple of minor bugs that pop up now and again. For example, if you put the iPhone's display to sleep before you start the workout timer, the app crashes. The audio alerts, which are very handy, can cause problems if you're simultaneously listening to music (but usually they work just fine).
And the big drawback of this solution versus a good GPS watch from Timex or Garmin is that the iPhone isn't a very convenient running buddy, and it certainly doesn't play well with water. So it's not a real multisport device. But in the end, if you already own an iPhone or iPod Touch, the Wahoo Key and its corresponding app make for an absolutely fantastic ANT+ head unit. It's very cheap, when you ignore the cost of the phone, it works brilliantly, integrates with TrainingPeaks (or will email you your power data directly for use in other applications), and just makes life easy. Obviously, it's not the simplest solution if you don't already own an iOS device, but if you do, you're in for a treat.
Feature-packed software, minimal added hardware
Makes great use of the large iPhone display
Send workouts wirelessly to your computer
Cheap (if you already own the iPhone)
Doesn't stay on your bike
Software integration could be refined
Inaccessible (if you don't already own the iPhone)