Yes they are completely safe to use for sleep...just not safe when driving or operating heavy machinery I would assume.

Having a song on a loop will not cause you to become stuck in a dream lol. They might help you get into the correct brain state for astral projection more quickly, but when it comes time to wake up...there's no way that binaural beats could interfere with the brains natural REM-sleep-off mechanism, which is hormonal. The binaural beats can assist normal brain functioning symbiotically, but they aren't strong enough to interrupt or interfere with those same brain functions. That's why they only work when attempting to get into a particular (theta) brain state.