What is unsafe about cell communication is that there is virtually no way to prevent being tracked. Bluetooth is not necessarily more secure but has several advantages:

1. Its Mac address can be easily changed. With a fake Mac address it's more difficult to track someone down, albeit it needs some "technical skills" (going in the developer settings)
2. With these apps communication is encrypted by default unlike cell tower communication
3. The range is limited. If police listens over Bluetooth they'll be able to track less people down

Not at the same scale as mobile traffic

Bluetooth by definition doesn’t go much past 10-20 meters

Super easy. You can also do basic triangulation with some specialty hardware.