Having heard ones say that there is no difference in speed with combo blades, I did my own little experiment with 2 Neubauer Titan blades about a year ago. Had long pips and short pips on each, but on one of the blades I put the long pips on the 'fast' side, and the short pips on the 'slow' side. There was a noticeable difference in speed between the two blades. Could repeatedly have the 2 blades handed to me without knowing which one was reversed, and could tell each and every time by how they played.
Having said that, I agree that the difference isn't as great as probably hoped for, but there is definitely a difference, which may make it worthwhile for some to use a combo blade. I only tried it with my Titan blades, as they are the only combo blades I own. So it's certainly possible that with many combo blades the difference might be so small that it's not worth it. Just my experience...