Basically, though magic does challenge logic, it eventually mutates the body when it is used too much, causing people to become big murderous insane monsters that cannot be turned back into humans. To be able to use magic without turning into monsters, they developed the molds, which are small mecha armors.
The story revolves around a man who feels guilty over an event that is later revealed about his past. He has adopted a little girl who was born partially mutated from a human mother and mutated father. This further makes him question if there is some humanity left in the rampaging monsters.
The story deals with a plot of how people's greed cause them to put lives at risk, terrorists fighting the police force and society holding on to the belief that they have no choice but to do certain things to console themselves and justify the actions taken against those who were once humans.
The setting and somewhat systematic approach to magic reminds me of Fullmetal Alchemist, along with the hidden plots and guilt trips, and the occasional mutated human, though Strait Jacket is far more violent and bloody.
I never liked random magic and like it when they give some sort of explanation, even if magic is still magic and defies logic, there are certain established boundaries to it, which allows viewers more insight into the world were the story takes place and more chances to speculate about the upcoming plot twists. This is always a plus to get into the plot, maybe even a necessity for some, myself included.
The art and sound is very good, no complaints there. The story is short, but it does pack a good plot, it feels more like a movie than an OVA. Overall, it is a good anime and worth watching.
