exhaust vent?

would using an exhaust vent with flaps be a bad idea on a RMH that extracts enough heat?

seems like it could stop your air flow from reversing, and also limit airflow while the RMH isnt being used.

https://www.amazon.com/Lambro-Industries-Plastic-outside-dimensions/dp/B00AFCH78G

only possible issue i could see is that it might make the fire harder to start?
could the last little bit of your exhaust get stuck?

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.