Actually, I find that switching from left-to-right works to even out the wear even if the tires are directional. For daily drive, its ok and very little difference, only in very hard driving will one notice the difference in traction quality. But since the tire is 50% or more worn, one cannot expect high-quality traction anyway.
You can test the stopping distance as well. Its about the same in dry roads. I do ABS stopping from one speed-bump to the next speed bump. Accelerate to 50kph and hit the brakes hard, see how far you are from the next speed bump. An easy measure.