I take my hat off from these guys. Knowing how hard is to do video processing in Android, kudos to the team.
It already has 20k ratings in a day, which from my experience can be around 1M and a half users. I cannot remember any other app which got such huge start. And word of mouth, basically.
Freepik
Freepik
Relayo
Bumpn
Freepik
tl;dr Marketing