The Bike tile was added in the big update in Jan or Feb--before then most people would have been using the run tile for biking. I'm not a hard core bike rider, but do ride up to 40 km or so for exercise and ride to work a few times a week with a 20 min ride. For a very hard core competition athlete, it likely doesn't replace something like PowerTap or similar with route data, HR sensors and bike sensors measuring watts applied to the cranks.
However, I think it compares very favorably with Endomundo as a great solution for someone who rides for exercise, but isn't a competition athlete. For my exercise rides I have been using my bike computer, Endomundo, and The Band Bike tile to compare. I think the elevation data is better with Endomundo, but I only get the HR with the Band. Getting updates on the Band is also useful. I usually have my Band on the inside of the wrist, but for biking I flip it out like a watch. I've been wearing a couple layers of jackets or long sleeve shirts for more of my rides, so that makes it a little hard to read the updates. Should work better as it warms up.
Some have criticized the accuracy of the Band's HR monitor, but here again, I think if you are a super serious competition athlete you will spend more money for a more accurate set up. If you want to know what your baseline is and how your recent work outs compare with a month ago, I think the Band is great for that.