Just installed mine, definitely more airflow through the ducts. Noise is probably about the same - seems most of the noise is from the intake air crossing the cooler which you cannot really reduce without also reducing airflow.

Install was super easy and in my case I did not have to remove the existing duct terminations or cut the box sealing off the opening despite the directions saying that. I did have to move one of my AC units 1/2" but that was simple since I had the 4 bolts and ceiling flange off anyways.

I would estimate you could get 50-80% of the same outcome with a DIY approach but will not match the precision contouring of the foam insert from the Airflow kit. Just up to you on what your time is worth to try doing it yourself vs buying the kit.