GuestCorrectly
Bluetooth always runs my battery down too quickly and coupled with the fact I only switch data on when I need it as I (gasp!) use pay as you go, can’t see it being effective on my phone
The app doesn't use data to identify if you are close to someone so it doesn't matter if you switch the data on or not. Use wi-fi when you get back home and the app should sync all the relevant data.
I'm guessing you may have a very old phone as new Bluetooth versions don't run down the battery anything like the old one, but if you have a phone that can accept the app then you shouldn't see any adverse impact on your battery.