Many online muters re-encode the entire video just to drop the sound, which is slow and shaves a little quality each time. Flippy runs the copy-video, drop-audio recipe instead: the audio track is removed from the container and the video passes through untouched.
The result has no audio track at all, rather than a silent one. Players handle that fine, but a few editing timelines expect every clip to carry audio: if yours complains, add a silent track inside the editor rather than re-uploading.
Keep the original if you might want the sound later. The muted file has genuinely lost its audio: there is nothing left in it to recover.