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.
You have to be odd to be #1 - Seuss. An odd little ad:
montana community seeking 20 people who are gardeners or want to be gardeners
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