R1v3r, my BTRFSchecker work in this way:
1. It check what the current state, same command as you wrote manually:
2. If option "Run balancer when needed" is activated and allocation more than 13153337344 or 89% it automatically will start balancer command from official /lib/systemd/system/btrfs-balance.service file that disabled by default:
3. If allocation less 13153337344 or 89% and "Run balancer when needed" activated, script look on slider value and change it in the command:
That all