I use GrillGrates flipped over (flat side up) 100% of the time. You get all over searing and it's super easy to clean that way. I use a bench scraper and scrape off all the crud. I never have to worry about small food falling through the grates. Plus it traps heat so the plate get much hotter.

I find GrillGrates flat side up are better than the Grate Griddle b/c the holes in the GrillGrate lets excess juices run off (I'm Korean so I cook a lot of marinated meat). Also, I replaced all of my grates so it covers 100% of my grill. If you try that with the Grate Griddle you'll get bumps where the plates connect with each other. That doesn't happen with the Grill Grate flipped upside down.

If you don't want to cover your entire grill you can also just buy a cast iron or thick carbon steel griddle that's not specific to the Weber and just put them on top of the existing grate. It'll be much cheaper that way. Or just buy a frying pan. The following is just an example.

https://www.lodgecastiron.com/product/pro-grid-reversibile-grill-griddle?sku=LPGI3

Or you can get a griddle top.

https://www.amazon.com/dp/B07GDJW3CL

You can even go to a metal shop and have them cut you a piece of raw steel. People do that to make pizza / baking steels. You can do that for griddles as well.