I have seen the Windbeater do a good job in eliminating the backup of
smoke into the living area due to trees deflecting certain directional
winds down at a chimney and pushing the smoke back into the house even
though that same chimney drafted nicely under different wind
conditions.

But if you are looking for it to stop cold drafts from blowing down the
chimney when the fire is not lit, you will be dissapointed. That is not
what it is designed to hold back. Only a lock top or chimney balloon
will help that.