I smoked a batch of Kokanee Salmon today, and the fan makes the temperature and smoke levels in my smoker much more even. Before I added the fan, sausages or fish would smoke and dry out at considerably different rates at different levels in the smoker. I had to rotate the racks top to bottom periodically to compensate for that problem. There was also a difference from side to side in the smoker. The smoke seemed to come out of the generator and head straight for the vent. Fish or sausages that weren't on that route didn't get nearly as much smoke, and didn't dry out as fast. So I also had to rotate the racks 180 degrees.
As an experiment, I didn't rotate the racks when smoking this batch of Kokanees. I can't see any difference between the fish which were on different racks, or on different ends of the same rack, which was certainly not the case before I added the fan. I'm happy about this improvement in performance, and think the fan was a good investment. Kokanee fillets are quite thin, so I don't know if the fan reduces the length of time required to dry out meat. I'll have to try some thicker fillets or some sausage to get a feel for that.
To quantify the difference between the performance of my smoker without a fan and with a fan, I could put temperature probes at various locations inside the smoker, and measure the air temperature in the smoker with the fan off and with the fan running. But based on how evenly this batch of Kokanee got smoked, I know the fan improves the performance of my smoker.
To see how the fan circulates smoke inside my smoker, I'm going to get a piece of glass about the size of the door of my smoker and clamp it over the front of the smoker. That may help me decide how much space I need to leave between sausages or fish fillets to allow even distribution of the smoke.
The fan blade I bought looks bigger than most of the fan blades I see in pictures of the fans which other people have installed in their smokers. Kirby (pikeman-95), on the other hand, has several big fans in his smoker, which probably get the smoke moving like a hurricane in the smoke chamber. If I had access to various sized fan blades, it would be interesting to change blades to see how the performance of my smoker changes.