With 4" filters is there an easy way to measure condition?

I switched out my 1" filters for 4". Since they are expensive. Is there an easy way to figure out when they need changing based on air resistance? Is a manometer before and after the filter the best way? I saw a wireless module that is about **** which is ok but they want a subscription fee to use it. My return is a 20x25 with the outside gas/electric package unit outside about ~ 25ft from the air filter.

source https://hvac-talk.com/vbb/threads/2235971-With-4-quot-filters-is-there-an-easy-way-to-measure-condition?goto=newpost