They're both good products, but just so you know, neither set-up is going to turn your grill into a 22.5" WSM. I've checked out both, and if not mistaken, capacity is less on the EZ for how it cooks. However, I spoke on the phone with the inventor a while back, and you couldn't buy from a finer gentleman. Even with all my grills and smokers, I wish I could buy one from him, to tell you the truth.
Folks report that temp control is harder on the CB than on the WSM, at least if your grill has the OT sweeper system. I'm sure it's a good product as well, though. I've got CB doors on both of my wsm's. Do some searches and you should find a lot of old posts on both.