Running a solid pushrod back unsupported (getting supports in can be a real pain) can be an issue with vibration and eventual failure at the end of the pushrod. If that happens your only link to the elevators is gone!!! BOOM no more plane.

At least with pull-pull back to the bell crank both cables would need to fail, if you only break one at worst you could land inverted (or at least give it a shot) and have a chance at saving something of the airplane. Plus cable will stand up to the vibration a lot better than a massive 30" long pushrod will over time.

I have used the MK bellcrank in 5 airplanes 4 being with Centrals 3/16" carbon rod from servo to bellcrank, never had one fail, but my comfort level is much much much higher now that I have pull-pull. More confidence in your setup breeds more confidence in your flying.