Mirror is the latest fitness craze. It’s a unique exercise apparatus that allows you to focus on your reflection and the instructor at the same time. It's like having the best spot in the class with ...

This is an installment of Good Fit, a column about exercise. At Form Fitness, in Brooklyn, you’ll find an assortment of squat racks, dumbbells, and pull-up bars—which is to say, it’s a typical gym.