I have Excel stovepipe, and requested installation of their stovepipe damper with the stove. I have regretted not having taken it out of the box and looking it over before the install guys put it in. I've not had my stovepipe apart to inspect/clean this season--(tried, but the telescoping section did not easily yield to my attempt, and I decided it wasn't broke, so I wasn't going to fix it until spring). When I do, I intend to look it over carefully, but the pix I saw at their website show no perforations in the actual damper. I'm concluding that the stops on these (you can only turn it a quarter-turn) must be intermittent, allowing for air movement around the outside of the pipe (which makes sense in terms of preventing creosote buildup on the pipe--I think). These are pricier than most dampers I've seen, but it did not make sense to me to buy an expensive stove and chimney and cheap out on the damper.
I've been very glad that I bought and installed this damper. Didn't use it at first because Stove Store Guy said it wasn't recommended for my stove. Then Stove Store Owner said, "Use judiciously," and I have, ever since. Keeps my house warmer, makes fires last longer, and I have no evidence of creosote buildup. I throw one of those creosote-prevention bricks in once a month, per recommendation of SSO.