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You can put a lump reducer in an XL. They haven't made a lump expander for any Egg as of yet. The extra area of an XL is good to have at times when you have a large group of folks. Buy the largest you can afford.
I initially purchased the platesetter when I bought my XL. I would have been money ahead to buy the Woo/AR in the first place and not had to throw away a bunch of cobbled together junk to do what this combo does with elegance. Next to my Thermapen the best accessory I bought for my Egg. The combination allows you to do any combination of cooks that the Egg is capable from wok to low level sear and to raised grid and multiple racks or anything you might dream up. It's a little pricy but worth every penny in my estimation.
I also have the Lodge Double Dutch 5 qt. L8DD3. Versatile as you get three combinations with the 2 parts. The lid id a skillet, the base is an open deep pot and together they are a Dutch oven. Also not much more expensive than a conventional DO.
Be aware that certain surface types can be very misleading on IR temperatures. Generally dark, matte surfaces give fairly accurate readings but highly polished light colored ones can be quite a way off. Most of our grill stuff will be close enough if it has been used a while but a brand new white pizza stone might be off a little. Shiny metallic objects are an issue, think one of those highly finished All Clad stainless steel frying pans. I recently purchased a new espresso machine and the copper boiler is giving false readings on the IR. Better quality guns have a correction factor that can be plugged in as emissivity to compensate for these factors but most times it is not a big deal unless you put your fingers on the frying pan that reads much cooler than it actually is.