Depends on the quality of the filters really. Also helps if you put a shroud on the box fan so you don’t have backflow around the corners.

https://www.texairfilters.com/how-to-improve-the-efficiency-of-the-box-fan-and-merv-13-filter-air-cleaner/

Effectiveness is pretty much entirely dictated by what filter you choose, assuming you don’t mess up building it and leave huge gaps. This guy on youtube made a video showing the effectiveness of different filters: https://www.youtube.com/watch?v=XAJ__E-hIJc

I have one with just some cheapo filters in my workshop. Does a great job of keeping dust out of the air for paint and finish work.