A "nitrox stick" is nothing more than a pipe that thoroughly mixes air and oxygen before the mixture is fed into the intake manifold of a compressor. There's nothing special or magical about it.
The baffles inside of the nitrox stick that mix the air should be made of a material that is easily cleaned to oxygen standards and does not feed particulate matter into the compressor. For example, foam or fiber would be very poor choices for baffle material.
Usually there is an oxygen analyzer between the nitrox stick and the compressor, so that you can measure in real time the Nitrox mix that you are creating as you feed in oxygen.
Too many baffles, and the compressor has to pull too hard to suck air through the nitrox stick. Too few baffles and the air and oxygen is not mixed adequately, resulting in spikes of oxygen going into the compressor (explosion hazard).
Ideally, a homemade stick would contain a repeating number of baffles like Wiffle balls that can be added to increase mixing or substracted to reduce resistance.
Here is my Nitrox stick. I have a lawn-mower air filter sitting on top to keep gross material out of the stick. I used PVC end caps with drilled holes as my baffles. Initially I had 4 baffles but there was too much resistance, so I removed one. I can set the oxygen valve and get a steady blend within 0.1% of my target.