Activated Carbon Filter and Fan Questions

I'm looking at the small fan and filter combo that HTG Supply sells, I think it's about 120$. According to the formula used to determine the size needed for a given space this should be more than enough. I have two questions. Is there any reason to go up a size to be safe? Does humidity affect the the effectiveness of the filter.

good to go bigger cause if u ever expand the grow area than your all set. also if you throw a fan speed controller in there will quite down noise