Hello Linne,
thank you for the feedback. Sleep tracking it definitely is not a gimmick. It is using actigraphy and there is planty of papers which show good results of this method for sleep tracking. Please see more details here:
https://sites.google.com/site/sleepasandroid/graphs.
Regarding battery use. Usually this is not caused by the sleep tracking directly as this is usually not consuming too much battery (according to our test sleep tracking does not consume more than 1-2% battery per hour of tracking on a factory resent Nexus phone), but because we hold a wake lock (keeping the phone awake) any other usually badly written apps may access the CPU extensively during the sleep tracking time. I would suggest checking which services are running before you get to sleep. For us it is hard to debug this. Also battery statistics are not a hint here as all battery consumption is accounted to the app which holds the lock even it did not consume the battery - this is by design in Android.
I good test would be to reboot your phone before sleep tracking (or kill any unnecessary services running) and see if sleep tracking will still consume so much battery afterward.
But if you like to skip sleep tracking altogether, no problem. You can still use all the features such as alarms, CAPTCHA, time to bed and related features, you just don't start sleep tracking and you can enter your sleep manually using the +moon icon in sleep graph screen.
Thank you very much.
Best regards,
Petr