Nothing is churning out new earbuds at a faster clip than smartphones. The company just introduced the Nothing Ear and Nothing Ear (a), priced at $149 and $99, respectively. Together, they mark Nothing’s fourth and fifth products in the headphone category. First came the original Ear 1, which stood out for its partly transparent design but suffered from bugs and inconsistent audio performance. Then, Nothing went after a different audience with the open-style (and oddly named) Ear Stick. And a year ago...