Product review (5 stars): Works great, I don't know why the hardware stores don't ...
Installed a downdraft cooktop that had an odd 5 in outlet instead of a 6 and there was absolutely no room to install a reducer.  At first we built a square duct box but then the client had granite counter tops put in.  I ordered this duct hose and when we reinstalled the cooktop we used this hose instead of the box.  Works great, I don't know why the hardware stores don't carry a 5 in flex duct.  Its just as durable as can be expected, the reviews stating its fragile must not be used to the nature of this product.