Pusher props are fine for aircraft cruising, say, around FL020 and below.

But at higher altitudes, the speed of sound is considerably lower, and the radial velocity of the prop blade tips start to reach sonic velocity, with the corresponding significant increase in drag, thus requiring more torque to spin at constant RPM, resulting in decreased fuel efficiency.

The test bed pushers on commercial jets were a far shorter set of (more numerous) blades for that exact reason. This particular aircraft seems to have a standard sized propeller, with a greater blade length, and corresponding greater radial tip velocity.