Hidden effect is supposedly +18 attack and +5 acc, activated at less then 100% tp(Along with the latent effect) and when doing weapon skills. So not good if you're waiting to skillchain, but decent if you're spamming rampage. Juggernaut's better of course, but jug is 7 million.
On a negative note it's just supposed to be a generic black axe, no cool red like in the icon.