I have Galaxy 4s and Fitbit Flex. Their step tracker figures are close, withing +/- 2-3%.

I mainly bought it for sleep tracking, but then I realized you had to manually enter sleep / wake up times for you to see any graphs. I don't know why there can't be some default value that can be algorithmically adjusted, because most people tend to go to bed and wake up around the same time.

Misfit basically does that. I think their pebble app does that too, but I hear about bugs with data syncing.

The Pebble app/iOS app syncing used to be buggy as hell (retrying a few times might get it to sync). The updated iOS app seems to sync reliably now.

As for sleep tracking, as far as I can tell you have to push a button at bedtime. Don't care much about sleep tracking, so I haven't researched to see that my assessment is correct. Still, not a big deal to me when I do use it.

It made more sense a few years ago when phones didn't have the ability to do constant motion tracking with very little battery use.