Designing BLE advertising: 31 bytes, intervals and privacyguide · unverified · Legacy advertising carries 31 bytes of data (plus 31 in the scan response); extended advertising in Bluetooth 5 carries much more. Pick intervals for discovery time vs battery, and don't rely on a fixed address.
iOS never shows the BLE MAC address: don't use it as device identitywarning · unverified · Core Bluetooth identifies peripherals by a system-generated UUID, not the Bluetooth address, and that UUID differs between phones. Put your own device ID into advertising data or a characteristic.