It's my understanding that Maxx will last longer than Camco, possibly due to UV resistance or type of material used. These covers allow the vent to stay open anytime or all the time for ventilation. No worry about rain coming in. Ventilation can be the key to stopping interior mold growth in eggs.
I have a cover/fan on my rear vent and a plain cover on my forward vent.
Windows are the slider type, so I can't leave those open, but my vents stay open 24/7 while parked in my back yard.