The battery pack has a USB-C and a normal USB-A socket. The specifications for the Elecjet state which standards are supported, namely Quick Charge 3.0 (USB-A), Pass-Through Charging (USB-A), Fast Charge (USB-A), and for USB-C Power Delivery 3.0, DC 5V/3.0A, DC 9V/3.0A, DC 12V/3.0A, DC 15V/3.0A, DC 20V/2.25A. Unfortunately, there is no information about this in the technical specifications for the iPad Pro. This is hardly surprising, as Apple only wants people to buy Apple devices and Apple accessories. A self-contained system. However, Apple will not want to move that far away from the standard in this case. It can therefore be assumed that the device will communicate and function in one of the protocols offered by the BatteryPack.

I would also like to point out that fast-charging brings the cells closer to the end of their life more quickly if used frequently. If you are not in a hurry, you should not "fast-charge" either.