The Windkat has no moving parts and is therefore one of the safest downdraft chimney cowls you can buy.
Chimney cowls with moving parts can be unreliable because they are prone to failure which can happen at any time. The reason they fail is they become choked with soot from the fire below. If you rely on a spinning cowl (that draws up air by spinning) or moving cowl (that adjusts to wind direction in anyway by moving), to stop downdraught and it fails while the fire is on, there can be serious consequences if the smoke cannot then escape.
Another common complaint we hear is that moving cowls and spinning cowls often end up making a very annoying squeaking noise as the bearings start to fail.