the eMMC replacement is quite an advanced repair. you need extensive practice with SMT Soldering techniques to do this properly. IF you want to go this way, i would suggest an electronics course through college before attempting, but you CAN train yourself via youtube videos.
you would need;
SOLDER
FLUX
SOLDERING IRON
TEMP/AIRFLOW CONTROLLED, CONCENTRATED HOT AIR GUN
HEAT RESISTANT SURFACE (TILE)
MICROSCOPE (OPTIONAL)
The board replacement is a better fit for first time repairs, but like you said, no one can guarentee the quality of parts you get.