I think they're interesting for about 3 weeks. Then? "Meh."
Motion-X is now making an app called "24/7" - counts your steps, tries to divine your sleep patterns (iffy), optimal napping, etc.
Only uses the iPhn internal motion sensors, no peripheral to wear. Under $10
As good as Fitbit? probably not. Just as useful? very probably.
These things are generally telling you things you already know on any given day. Good to focus on, undoubtedly, but interest wanes after a while.