Agreed, Rahock - the one thing that the additive claims to do that synthetic won't is to decrease oil consumption. That's why I included the mention of STP, which essentially just thickened oil so a loose motor wouldn't burn it as readily.
To me, oil consumption is what it is. You can change the viscosity of the oil you run (for instance, run 15-50 rather than 10-30) in an effort to reduce oil consumption, but until consumption gets to be more than a quart per thousand, I don't consider it to be a significant issue....and even then, if it runs well and doesn't foul plugs, just feed it oil and drive it.
Digression:
I once had a '66 GTO (389 V8, single Carter AFB carb) that had been run VERY HARD and hot, and when I got it, the oil rings had lost their temper. Honest to god, it burned a quart every 50 miles...and I could lay down a smoke screen by running the RPM up, letting up on the throttle for 2-3 seconds and then nailing it again. Compression and power were great, but those oil rings weren't doing much. I rebuilt it before long....problem solved.