The 4" Phresh filter I ordered arrived and the carbon was all broken up and leaking everywhere (Amazon reviews seem accurate). I tried to install it anyway but my ducting is 4" and even though they listed their filter as 4", it wouldn't fit.
I measured the filter where the ducting attaches and it was 4 1/8"....so I returned it.
I ordered a different filter and it's 100% better than my old Vivosun filter, eliminate my smell issues outside the tent completely and I'm in almost week 4 of flower.
Filter I am using and happy with: https://www.amazon.com/dp/B07VN4KL1B/ref=cm_sw_r_cp_apa_i_izhODb52XHD93
My only complaint is the prefilter doesn't have the cool logo on it, it's just plain white which really isn't a big deal lol.