If you're going straight-and-level and you move the wing up, lo-and-behold you're still going straight and level.
Must be a very different flexwing to the one I've been flying for the last 17 years.... The control bar does exactly the same as a normal control yoke or column, except it does it back to front compared to what you're used to. So push right and go left, push forward sky gets bigger, then if you keep pushing it gets MUCH smaller!! It's otherwise known as "Weightshift" - move the C of G around in a conventional A/C and it will respond accordingly, all we are doing is moving the combined weight of pilot, passenger, engine & fuel around to persuade the wing to fly other than straight and level. Change the power setting and it might initially seem odd, all that happens is that the trike will swing forward or back, and then the aircraft will climb or descend. Simple really!!