This chimney topper looks like it will be a permanent fix. The attachment is stable with 8 bolts to hold to the chimney pipe. Previous owner had a hard cap on the fireplace that required a trip to the roof to have fire. We like fires on cold rainy nights, not the best time to think about going to the roof. Unit appears durable and since it is stainless steel it will not require maintenance.
Bought this model in part b/c it appeared to have 2 screws on the long sides (6 total) to attach to the chimney flue. However, the 8x13 size uses a single screw in the center of each side, not the 2 pictured. The cap itself appears well-made, and so far I've had at least one very breezy day and it's still in place, but I did bed it in silicone caulk in addition to using the screws, and I'm sure that helps.
There was no existing cap on the chimney, only wire mesh to keep out animals. Purchased this product online - quick delivery (although it was loose in box with no packing). Solid, good gauge stainless. should last a lifetime. Easy installation - place on the flue and tighten the bolts. As the flue is oval and the cap is rectangualr, there are small openings in the corners on the underside; they're small enough I don't think it'll be an issue.
I decided to order this product from Home Depot because they were the cheapest and they offered free shipping
It is well built, looks sturdy and fits perfectly on top of my fireplace. I would recommend this item without a doubt
Look at the pictures and the work done...