Garmin is great at collecting data, but not so good at analyzing it. You might want to try Runalyze, which can import your activity data automatically from Garmin. They have a more sophisticated and transparent VO2max calculation, and after each race you can recalibrate the calculation based on your result. The predicted race times (derived directly from the calculated VO2max) are then much closer to reality.
Wall of text incoming. The iPhone already tracks most things that these "dumb" bands would track. I use mine to track steps (built in, read with a third party app), routes everywhere I go (Moves without an account), sleep (Sleep Cycle), and weight (Withings + Weight Diary.
I run a few times a week, do some workouts, and drive my road bike a lot. To track these I'm using iSmoothRun. I just found out about this app a few months ago. It's killer and much better than Runtastic or anything else. The only additional device I use is a Polar H7 to track my heart rate. This can be interesting and useful if you're training for some goals like weight loss or increasing your pace.
When I'm done I export activities to Dropbox, then import them to Runalyze. I only found out about this a few months ago. It's made primarily for runners but can track everything. A dream come true because it can do statistics much better than anything else. It's free and open source. You can make a free account. Or download and host on your own. It does everything right that Runtastic and the others do wrong. After using it for a few days you'll instantly notice it's made by runners. It's for real athletes. There's aren't a lot of social features apart from making activies public and posting a link to them somewhere else like FaceBook.