Make sure you are downloading the exact ROM of the device you want to flash because
You can also use tools like Miracle Box, infinity CMII, Volcano, GPG Dragon etc to flash or upgrade SPD devices
A51 runs on a 1.3 GHz quad-core with ARM Mali 400 MP2 Spreadtrum SC7731C
SoC. 1GB RAM and 16GB internal Storage. Preloaded with Android 6.0
Marshmallow. Standard connectivity present are Wifi, bluetooth and gps
available. Dual SIM standby (EDGE / GPRS, HSDPA+).