I have a small, one footer that i really like. my friend has a larger one with a diffuser and i really like how it fills with smoke. It starts really thick and creamy at the bottom and really slowly creeps its way to the top. Mine just fills evenly throughout the whole bong. My friends does have a diffuser, mine does not. Would that make a difference? if so, im not even sure if mine could fit a diffuser. it has a small glass down stem thats it.
Your talking about a diffuser as a downstem that just has holes in the end to break up the smoke a little more right? they make those in all different thicknesses and lengths, you shouldnt have a hard time finding them at a headshop. In my opinion they wouldnt really make a difference, if you have a downstem that just has a hole in the end you probably wouldnt notice any difference between that and one with a sealed end with a couple smaller holes.