These are completely safe. You can use them on Spotify, Apple Music, or YouTube without paying a dime, though you may need to credit the creator (check the license: CC BY vs. CC0).
Bounce a single vocal word with a long reverb tail, reverse the audio clip, and place it right before the vocal enters to create an automated transition effect. If you would like to expand your library, tell me: free acapella pack
Generous, themed packages (e.g., "1,000 free vocal samples"). These are completely safe