I used to have the Weber cast iron grate for my 22.5, and I got rid of it. I personally didn't see any benefit, and it was a PITA to maintain. If I used it, and forgot to bring it inside, I had to de-rust it and re-season it.
The seasoning just couldn't hold up to the heat of good steak level charcoal heat. I had to oil it after cooking, then bring it inside.
That's just my own two-cents. A lot of people love CI grates. It just didn't work out well for me.