While the effect and change to the belt is nice and you can use items or thrive on things like speed pylons or frenzied shrines, the effect unfourtunatly doesn’t always work. I don’t know about attack speed on gear pieces but external modifiers to attack speed, like skills and those aforementioned doesn’t always change the frequency of the autocast as it reverts or “forgets” about those external modifiers.
Please look also into if there is some conflict with Echoing Fury and Vigilante Belt, about 40% of the time it doesn’t update on the effect unless you self cast Fist of the Heavens in a wonky manner.