I have to say, I hate sleeves. I tried a Provari for the first time a couple weeks ago, and the owner had a sleeve on it. When you would let go of the fire button, the button would stay depressed because it would get hung up on the sleeve. As far as the finish on the Buzz Pro goes, you really don't have to worry much, it's extremely durable. The only thing I would worry about is dirt or other substances getting into the button or around the voltage dial, and a sleeve wouldn't help you with that. A sleeve in my opinion, addresses something that isn't a problem, while ignoring something that could actually be a problem.
Just my 2 cents.