Are All DIYs the Same? Poor Results from 还我蓝天

So the difference in performance between the Smart Air and the copycat is the quality of the HEPA filter.

How would a consumer judge the quality of a HEPA filter before buying?

Thanks!

Hi, what is the cost of the replacement filters for the Smart Air fans? If I want to purchase from you but then skip the shipping costs for replacement filters down the line, could I do that? If so, where would I find the right filter? I ask because this post obviously highlights the importance of getting the choice of filter right.