Safe and effective if your government takes the internet down. Not good for daily use for people you are not close to.
The problem is that a regime who this would be useful against would have the ability to surveil the people who use this by seeing all the bluetooth being yelled out. They may not be able to see messages but they can figure out which users are using the software and possibly arrest them later for interrogation.
This year a completely practical man-in-the-middle attack was found. It stems from the fact that Bitchat had no mechanism to verify the identity keys. As such, a MITM could easily pretend to be a starred contact with no way for a user to see anything is out of the ordinary. An attack like this isn't possible in many safe end-to-end encrypted chat services. I strongly recommend you avoid the app because you can't trust the developers to properly implement cryptography, which is kind of essential.
The problem is that a regime who this would be useful against would have the ability to surveil the people who use this by seeing all the bluetooth being yelled out. They may not be able to see messages but they can figure out which users are using the software and possibly arrest them later for interrogation.