Flyback can cause an array of damage from direct damage to circuits to welding relay contacts shut. By placing the 'MOV on' board to suppress that load you can mitigate long term damage. These MOV breakout boards are great for 12v solenoids and maglocks
The 'MOV on' board is a compact breakout board containing a Metal oxide varistor to allow easy wiring of junction areas susceptible to flyback. It is best to place these as close to the inductive device (maglock, solenoid, etc) as possible.