Duct booster fan vs axial

I am having a heat gain issue in my flex duct. Airflow seems good but I am picking up a lot of heat in the 45 foot run. It was suggested to try a duct fan to move the air faster through the duct so it won't pick up as much heat.

It was suggested I use an axial fan vs booster fan. I can't find much on the axial fans. Any suggestions as to which one I should use? Is it best to put it closer to the register or closer to the supply? It will be a 7 or 8" depending on where I place it because I have a reducer in the line