I love it.
It has a rather nice boon, and a rather brutal drawback which on its own makes it a pretty cool cursed item in my book. The way the curse and boon interact also creates another secondary curse of aggression in a way that doesn’t interfere with player control over their character is really neat.
If I were going to run this, I might restrict its boon to Kill conflicts to ratchet up the pressure, and/or make something neat happen to the body if the flail manages to kill the host.