You can feel the difference in drag using the aero bars. It's actually akin to drafting. I figure I pick up about 2 mph using the bars using the same effort. That being said, you don't want to use them in group rides, they get in the way on hills, they cause handling to be much more unstable, so unless you are racing where drafting is not allowed (triathlons or time trials) or just want to ride alone on flat straight roads I would keep them off. They also take some getting use to and need to be fitted properly to be comfortable. You might need to move your seat forward (which makes the handling even trickier) to keep yourself from being too stretched out. I used to triathlon and occasionally wish I had them on windy days riding into a headwind otherwise I am happier not using them.