I’ll assume you mean (released 2015). Here’s a concise, solid review focusing on the firmware experience.
The official software provided by ZTE. It uses the Nubia UI and is optimized for the device's hardware, including its specific camera sensors. z9 mini firmware
If your phone is stuck in a boot loop or you want to return to a clean factory state, follow these steps to flash the stock ROM. I’ll assume you mean (released 2015)
The Z9 Mini firmware plays a crucial role in ensuring the device's performance, security, and functionality. Regular updates and proper maintenance can help prevent issues and keep the device running smoothly. z9 mini firmware