I have heard mixed reviews about pushing or pulling and whether or not to put it on the same run as your lights or not. I believe all methods work, assuming you are moving enough air through it to take care of the smell you have. One crazy thing a hydro store guy told me is a solid price of carbon could blow through your lights and break a bulb, but I've never heard of it happening. So I have multiple filters set up in different configs. For maximum odor control, in a negative pressure environmentment, pull air through filter. Put whatever you want between the filter and fan assuming you have enough CFMs. Remember the fan must be equal or less CFMs than the filter. If the fan has more it will make the fan work extra hard and pit wear on the motor. Less will basically extend the life of the filter assuming enough air is moving to remove smells. Pushing through a filter works, but only if there is no other tiny gap in the room for smell to escape. Room must be air tight except the the airflow going out of the filter and an intake creating negative pressure in the room. This is pretty hard to accomplish in most circumstances. Or you can do what I did, get a filter 3x the size I needed with a fan 2x the size I needed taped to the top. This just recirculates the air in a 12x12x10 room that is kinda sealed, and no smells.
I recently switched from phresh filters to phat filters. The quality is prob only 80% as good but they are half the price. The filtering ability seems about the same but the construction is obviously just a bit jankier.