I have one on the top window in my 6X6 greenhouse and I find it very good. helps a lot to keep the temparture down. i also have lovre windows in the side but I open them manually, they get the air circulating through. i would say yes they are worth it. Had mine 4 years now you set it to the temprature you want it to open at by just turning the black handle thingy, its easy and it will come with instructions . You must protect it from the cold in winter I just wrap mine in bubble wrap and cardboard, making sure any wet can drain form the bottom and not freeze.
They cost £19.99 from an Argos Extra Store
__________________ Denise xox Learn from the mistakes of others because you'll never live long enough to make them all yourself.
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