[D-CEL]

Steel vs. alum flywheels. SFI/BLOWPROOF VS. OEM.

Yes it's very noticeable.
In a performance application, Aluminum is better, period. Not arguable.
They rev quicker, they are easier on the brakes, allow for better engine braking, way nicer to install when laying on your back under a car.
In the old days of drag racing, it was thought that a steel (read heavier) flywheel had an advantage in getting a heavy car with low torque and slicks out of the whole better. They thought winding up the motor up and storing the energy. The slicks could absorb the shock load and put the power to the ground, reducing 60" times.
The reality is, that advantage is quickly overcome buy the alum flywheels lighter weight, which is a huge advantage over the remaining 97% of the race.
With street tires that extra stored energy aids in breaking the tires loose.

SFI/BLOWPROOF VS. OEM.

You only need to see it happen once. It's hard to believe how much destruction results. It is exactly like a big fragmentation grenade going off. Very loud bang, big flash, lots of sparks, large pieces of jagged steel flying in every direction. They blow huge holes in everything.
My personal opinion is that they should be mandatory in Cobras because of passengers position relative to the flywheel. Mid thigh is a bad place for a 10lb piece of jagged steel going a couple of hundred miles an hour to strike.
What is the cost difference? Maybe $200-$300? Worth it to me, but that’s your call.
Sure would suck to blow the leg off (or kill) you girl friend or child, because you were trying to save $300 on a $50k weekend toy.

Not me