What the 600 V / 9 A rating buys you in a switching supply
Rds(on) is specified at 450 mOhm maximum with 4.5 A drain current and 10 V gate drive, which translates to roughly 2 W conduction loss at full rated current — manageable with the 25 W power dissipation limit and the full-pack's direct-to-heatsink mounting.
ST has marked the STFI12N60M2 as Obsolete, which means the manufacturer no longer produces this exact order code. The through-hole I2PAK package makes the part easier to authenticate visually than a surface-mount device: the laser etch on the package body should match ST's marking format for the MDmesh M2 series, and the date code should be consistent with the manufacturer's production timeline. Any lot with a date code after the EOL notice window or with inconsistent marking font should raise a flag.
Gate charge and input capacitance — sizing the driver
A driver capable of sourcing and sinking at least 1 A peak will switch this FET in the 50-100 ns range, which is typical for a 100-200 kHz switching converter.