The refinement value of magic device will have the same damage reduction effect as that of shield. Furthermore, the more MP left, the more often physical/magic damage will be reduced.
Magic Device
[This effect is only for magic device as sub-weapon.]
When taking a fatal damage exceeding your MaxHP, there is a chance that 1 HP will be left. But once activated, this effect won't activate for a while and you will also temporarily lose the damage reduction effect based on your remaining MP.
Toram Online