I think you're getting a bit too excited here tbh. Just for anyone who hasn't read the new talent:
It's more likely the buff will be refreshed with every melee hit rather than stack up and fill your insanity bar lightning fast.
At 9 insanity every 3 seconds you, assuming a vacuum where you're not casting other spells, that means it takes you at least 36 seconds to get to 100 insanity (or 21 seconds to get to 60+ if you specced LotV). I wouldn't really call that "immediately"
It's certainly going to make fighting against melee more fair and less frustrating though. Great tool to have!