I have to disagree with the assessment that this style spring is the only one that is effective on a rear suspension. My reason for saying so is simple. The style you claim is only "for looks only" makes a huge difference n how hard my cars launch, although I did have to cut and position them differently than they came in the box. Had I just bolted them on as they came in the box, you are correct. They would not have done anything.
That being said, we may be talking about apples and oranges.
My lower powered 408" Magnum automatic trans Mopar runs in the high 11's with them, and my 493" RB 5 speed Mopar runs in the 10's. Needless to say neither one is really a low powered car that has slapper bars just for looks.
I do agree that I was fooled for a long time by the bad reputation these bars had. Then I remembered virtually every set I had ever seen on a car had 2", 3", 4" and even 5 inches or more gap between the snubber and the bottom of the front spring eye. No wonder they didn't do anything. The snubber virtually never touched the bottom of the front spring eye to stop the axle wrap and push the tire into the pavement.
For these bars to do their work, they must be properly adjusted as shown in these pictures. In both of my cases, I had to alter the rear bar attaching point by cutting and welding to get the rubber snubber into position. I assume that is what all that additional j-bolt strapping hardware is trying to accomplish on the fancy version you posted. It appears that once the other version is bolted on, that nothing moves or pivots once tightened, but I've never used that style.
I run a pair of 3200lb passenger side SS springs in both my 3700lbs cars. They needed something to control the spring wrap I was inducing with the higher power outputs I run. Turns out, these properly adjusted slapper bars are perfect for the job. Pinion snubbers and Caltracs are just too brutal of a ride on the street for me.
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