JonE,
I have a CS55 and the large Grill Dome ceramic cooker which is a twin to the Green Egg. For real long cooks like beef brisket - 18 to 20 hours I like the Grill Dome. The brisket will not pick up as much smoke as the CS55, but it gets enough. I do have to use the double shelves to get a whole brisket in, It must be cut in half, one half for each shelf. I also have to use a throw away pan under the brisket to separate it from the charcoal's direct heat or it will get hard on the bottom.
When I am smoking fish, prime rib roast, pork roast, Cornish hens or turkeys where I want more smoke flavor and a shorter cook time I like the Cookshack 55. For ribs I like either cooker, but I can hang three times the ribs in the Cookshack model 55 (six whole spare ribs). In the Grill dome I have to lay the ribs in a rib rack and two shelves worth won't work.
Also, the CS55 is easier to use and clean, but I have use for both and enjoy them both. The CS55 gives more smoke flavor and the Grill Dome more of a BBQ flavor. I use a TEC grill for quickies like steaks and hamburgers.
Hope this helps. My wife complains about all my cookers and smokers - have six, but you can't be too rich, too young, too good looking or have too many cookers.
She qualifies for the first three, I only make the later.