Flatiron is one of the most sought after destinations in Manhattan for reasons including an abundance of restaurants and entertainment spots, the Union Square farmers market, Union Square, Madison Square Park and of course, Whole Foods. Whole Foods may not technically be in Flatiron but it's one block away hence for this purpose, I am including it.
Danny Meyer's Union Square Cafe by Union Square West was one of the early pioneers in driving up the neighborhood. The restaurant was rated #1 by Zagat for many years. Blue Water Grill, Eataly, Gramercy Tavern, Craft are other popular restaurants with the Flatiron ambiance. Paragon Sports Shop on Broadway is the coolest and largest sports shop in Manhattan. While across the street on Broadway is Beecher's Handmade cheese offering many top quality (and quite expensive) products for the cheese connoisseur.
The Union Square Farmers market offers a large variety of local and organic produce. Walking through it is a nature-like experience in the city sense. Chefs in nearby restaurants are often seen shopping there.
The factors above improve lifestyle which in turn drive property prices. Condominiums in Flatiron include pre-war 260 Park Avenue South, the new 15 Union Square West and pre-war 225 Fifth Avenue, at the northern edge of Flatiron.