If the 300 series is the same as the 200 series, each of the paddles should have a small A or B molded into one of their ends.
If you run it with an A-B paddle set (which is the default set up it is packaged in), it would push water forward strongly with both paddles when in the + range, then when it switches to the - range it will push water weakly in the reverse direction creating a weaker gyre in the opposite direction. The 'reverse' gyre is weaker because of the curve of the paddle blades is designed to push water primarily in the + direction.
If you swap out the one of the paddles to run in either an A-A or B-B set, one side of the gyre will push water forward while running in the + range. And at the same time the other side of the gyre will push water in the reverse direction creating turbulent flow. When the gyre switches to the negative range, the flow switches: the side that was pushing forward will push in reverse to create turbulence on that half of the tank, and the side that was creating turbulence will push forward.
This CoralVue vid can probably explain it clearer:
https://blog.coralvue.com/cvtv-episode-3-maxspect-gyre-alternating-gyre-mode/
As far as wear and tear: The change in direction is created by the drive magnet simply spinning in the opposite direction. It's no more wear and tear than it switching from stopped-to-forward, stopped-to-foward or low-to-high, low-to-high when running in one of the other modes.