Enerox, page-4

They are different types of flow battery: Vanadium Redox is a true flow battery - electrons flow across a membrane during charge/discharge. Battery capacity (kWh) can be increased by increasing the size of the electrolyte tanks. Independently, power (kW) can be increased by adding more membrane. So capacity and power are independent of each other.

The Redflow ZBM on the other hand is a Hybrid flow battery. The battery is charged by plating zinc metal onto a physical electrode stack, so you can't necessarily increase capacity by simply increasing the electrolyte volume - you also need to increase the capacity of the electrode stack to accept additional zinc metal.