I think it's a tricky line between helping to keep room air from escaping, and hindering exhaust flow at startup and possibly running. The prevention of downdraft is obviously a good thing no matter what.
In any event, I wouldn't use one that had plastic involved, but stick to all metal, just in case.
Sure, he can talk to fish, but don't ask him what they say. You're better off reading a tiny ad:
It's a bit like "run away to the circus" but with gardening
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