A girlfriend of mine used one for a long time but didn't really like it. She said the clip kept coming undone during activities and she eventually ended up buying a Jawbone UP bracelet. I have one as well, here's review on HubPages: Better? :) http://fitgadgetreviews.hubpages.com/hub/The-new-Jawbone...

Here's a quick link with a review of the Jawbone UP. It works for Android and iPhone users. I've been using mine for about 6 months now and it is absolutely flawless. It monitors cardio activities perfectly as far as distance, caloric burn and intensity. http://www.fitgadgetreviews.com/jawbone-up-re...