Primo Searing Grate, Cast Iron, for Oval X-Large

Which Primo does this searing grate fit?

The Oval X-Large, which includes the Jack Daniel's Edition since that is an X-Large with a different finish. Primo cuts the grate to each firebox, so an X-Large grate belongs in an X-Large and nowhere else. The size in the title is the only fit information you need.

What is the point of a second grate just for searing?

Contact heat. The standard grate is thin and light and gives up its temperature the moment cold meat touches it. Cast iron carries far more stored heat, holds it under the food, and keeps the contact points above the temperature where browning happens. That is the whole difference, and you can see it in the marks.

Can I sear on one part of the grill and cook indirect on the other?

That is a sensible way to run it. Bank the coals so the fire is concentrated under the searing grate, sear there, then move the food to the cooler end of the grill to finish gently. It is the standard two-stage approach to thick cuts, and it needs no extra equipment beyond a way to move food.

Do I need gloves to take it off mid-cook?

Yes, and heavy ones. Cast iron stays hot long after the fire has been shut down, so it is not something to move casually. Plan where it is going before you lift it, and give it somewhere heatproof to sit rather than deciding once it is already in your hands.

Will it work with the cast iron griddle at the same time?

No, not on one level. The cast iron griddle and this grate both want the space directly over the fire, so you choose one per stage of the cook. Searing first and griddling second is the sequence most people settle on.