I have made my own using DIY methods and also purchased a Phresh 200cfm filter. The Phresh works great. ZERO smell... like a nuetral type smell coming out of the duct. I cant see the Phresh not working since mine works so well. The DIY worked for a bit but lost its power after 2 cycles. On top of that the Phresh is tiny in comparison and weighs barely anything. I can mount it almost anywhere and not worry about the weight.

It is very important that you match the CFM rating on your filter to the CFM rating on your fan otherwise you arent letting the filter work properly and the smell is likely to escape.