Are E3s worth it?

I tried a set on an 1989 Dakota with a 3.9L 5 speed. Figured it was cheaper to try it on a V6 first than a V8, lol. Didn't feel any difference in power, or gains in fuel economy. Not sure if it was because of the OBD-I PCM and TBI injection. But shows on TV claim gains. So my experience on the one vehicle I tried them on wasn't worth. What are other people experience?