We have one and it is fantastic! The large size is the best for our family of 4 and for fitting trays and pans on. I hated using our gas grill, was always a bit scared of it but am very happy to use our egg. It fires up so quickly we can use it midweek as well as weekends as happy to leave it doing it's thing while we get the kids in bed, does not need constant attention once the temp has stabilized.
There are recipes and lots of chat here:eggheadforum.com/
Would not bother with the official cookbook, once you have figured out what set up you need i.e. direct/indirect and the configuration of the plate setter you can just cook as you usually do. DH and I are in an unspoken competition to see what we can cook on there and no fails so far.
We use it several times a week and have done a variety of stuff on it including baking bread and biscuits - mostly for the novelty but partly because it was still hot from cooking pizza for lunch so why not?. You can use it like a convection oven, I did a full roast dinner on it at the weekend (chicken, roasties, yorkies, carrots, kale) as a test run for Christmas dinner.
It can do loads more than steaks and burgers. We have done chilli, lasagna and shepherds pie on it from start to finish in a cast iron dutch oven. In my DHs words the chilli was 'epic'.
If you need help getting started with the set up or some ideas you can message me directly from here I think.