For nearly two years, Alphabet’s drone company, Wing, has managed deliveries for a handful of Walmart locations in the Dallas-Fort Worth area. Customers in the metro region can click “checkout” on a small order on Walmart’s website or app and, within an average delivery window of 19 minutes, see a drone buzz above their lawn or backyard and lower a delivery box on a tether.

Now both companies say the service is ready for serious expansion. They announced Thursday that Wing’s drone delivery service will roll out to 100 additional US stores in the next year, including Walmart locations in Atlanta, Charlotte, Houston, Orlando, and Tampa. The companies say the expansion will give “millions” of homes access to drone delivery within 30 minutes or less, making the drone delivery network the largest in the country.

The expansion will test shoppers’ enthusiasm for super-quick deliveries—and communities’ interest in sharing airspace with a new kind of delivery vehicle. It will also likely help both companies analyze the commercial viability of drone delivery services, which have rolled out to a handful of areas across the world—including northwest Arkansas, metro Raleigh, North Carolina, and Lockeford, California, plus parts of Australia, Finland, Ireland, and Rwanda—but have yet to transform how global consumers think about quick delivery.

Some critics who have studied the drone industry doubt routine deliveries can become truly profitable. “It’s unlikely that it will become commercially viable in the foreseeable future,” says Matthias Winkenbach, who directs research at the MIT Center for Transportation & Logistics and has written about the industry. He cites regulatory hoops, the high costs of employing drone pilots, and the challenges of working in unpredictable situations with unpredictable people—namely, customers’ homes and customers themselves. Plus, he says, it’s hard to beat the efficiency and price of a “good old UPS truck.”

Wing says it will use what it’s learned about drone delivery rollouts in Dallas to quickly bring its services to other cities starting in the coming months. In that region, 18 stores are equipped with 18 drones each. Together, they deliver about 1,000 orders per day, says Adam Woodworth, the CEO of Wing. Top deliveries include baby wipes and eggs, he says, plus the items a person might not normally get delivered but want right now: a pint of milk because the kid wants a glass, or a forgotten recipe ingredient. At most stores, Wing workers pick, pack, and deploy drone orders; the plane-like drones, which have a five-foot wingspan, can carry packages weighing up to 5 pounds.

Parts of Dallas have access to drone deliveries of a broad selection of items for a fee of $20 per shipment, which is discounted to free for members of the $98-a-year Walmart+ program. A limited selection of items—generally priced no differently than in Walmart’s stores—are available to all customers for free delivery from Wing’s app. In initial expansion locations, only the latter option of ordering through Wing’s app will be available.