It’d be neat if the grinder had some sort of counter on it, perhaps when you hover over it in your inventory?
Very late edit: The Grinder works based on I believe the percentage of the kill you get, the same way you get XP. This is just speculation, but after some testing (having two people in a party, and one person not in the party, with the two in the party doing almost all of the damage), I’ve come to this conclusion. The percent of a “kill” you get with the grinder you get is how much you get towards your grinder. With this being the case, I could see how a counter would be hard. The best way to solve this would be to have some sort of simple visual clue on the actual model of the grinder, like a feint glow that gets brighter and brighter the closer it gets to popping, and also having a percentage gauge when you hover over it in the inventory, similarly to missions.