They are definitely worth it. No, they are not going to magically blow cold air. But, moving warm air is better than still hot air.

I did the Cobra Earl kit way back with the plastic blast gates and the plastic RV effluent hoses. Stay away from both of those. The blast gates eventually jammed, and the hoses melted above the headers on a track day.

I then used metal exhaust cutouts that I got on ebay. They had motors on them, but I modified them to use the cables. I replaced the tubing with high temp tubes from Pegasus Racing. I am happy with how these work.

The bilge blower fans aren't the quietest thing. If anyone has ever found some quiet ones, I would love to hear about them.