Among Lenovo’s brutalist and utilitarian ThinkPad lineup, popular with businesses or in any field in which an affordable and durable laptop is necessary, one particular ThinkPad stands out—the black sheep of the family that dropped out of engineering school and eventually graduated from design school by the skin of its teeth: the ThinkPad S431. It’s still not quite as stylish as some of Lenovo’s Mac-ripoff IdeaPads, and it still sports some of that red-on-black flair popular with baddies from...