"On Rampage" effects on unique items

Is "On Rampage" for each kill during rampage, on each rampage tier, or only when you first gain rampage?

As an example, this effect from Null and Void gloves "Gain immunity to physical damage for 1.5 seconds on Rampage". How often will this effect trigger?

On Rampage means every time you reach a new rampage tier.

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MonaHuna#6449 wrote:

On Rampage means every time you reach a new rampage tier.

So after 520 Rampage, I no longer gain benefits from "On Rampage" effects and should let the Rampage end and start it again?
I'm just trying to decide if it's worth getting Null And Void gloves on a build where I'm regularly hitting the 1000 Rampage cap within 20-30 seconds.

While you don't get any further "on Rampage" effects after 520 rampage, you still do get the inherent Rampage movespeed and damage increase.