You can produce some ammount of lift with a flat plate wing, some popular planes like the PA18, Aviat Husky or Christen Eagle use them on the horizontal tail and it produces enough lift to maintain moment equilibrum and allows control of the airplane.
But why should you use such a wing ? Where is the benefit ?(besides ease of structural design and reduction in tooling costs, making this one a perfect homebuild
)
Biggest problem might be the extreme hysteresis in the CL-alpha-curve, you might reach Cl max of about .8 if the leadng edge is rounded propperly, but you´ll have to reduce alpha to essentially zero to achive reattachment of the airflow once you are stalled. Additionally CL max will depend highly on leading edge contamination, making the flight characteristics of such a plane suitable for suicidal purpose only because you never know your stall speed when landing.
By the way, the Extra 300 has no dihedral, no camber and no twist like most of the aerobatic planes.