Highly suspect reliability
Having worked in BLE bluetooth with beacons for a couple of years, i have yet to see a single person get anything reliable out of the RSSI (relative strength indicator). It is the dream we all have to be able to make bluetooth beacons a reliable discovery product (and no, not for nefarious reasons). One minute a beacon is 5 metres away and the next it has magically moved to 15 metres. So effectively working with dozens of different broadcasting handsets rather than just a single beacon from one manufacturer, well,... I am highly doubtful that this app will be reliable.