Yes, contrarotating props with 2 electric motors would be efficient, and less complex than a contrarotating PSRU, but my comment was about noise. The 2 blades passing simultaneously through the wake of the vertical stabilizer increase vibration & noise. 3 blade prop adds a blade, hinge, & larger hub. Should be a simple bolt on.
This vehicle is a motor glider-most of the time it will fly with engine not in operation. Prop efficiency and noise is less important than simplicity and light weight and mainly low drag when not running.