I have a 22" which I use with a DigiQ2 and it is fantastic. We use it in comps as well as in the backyard. It is extremely helpful in long, cold weather cooks and when it is really loaded with meat. As so many have said it is not a need to have but is most definately a nice to have. It took me a few times of trial and error to figure out why I was getting temp spikes using the guru and what I learned was it was the air leaks around the base, the door and the lid. I applied some BGE felt gasket around the door and the inside of the lid and use some folded foil around the base to give it a nice seal and it has been tight as a drum eversince.
I will tell you I also have an 18" that I do not use the guru on for when I want to cook without it.
I would strongly recommend it as an addition at some point down the road. I also have the 10 CFM fan and it is a champ.
Stumps Elite 7, 22 & 18 WSMs, La Caja China, Bubba Keg, Weber Kettle, 180 Brisket Club