When Chinese tech giant ZTE started selling phones in the United States, it pounced on a niche market and stuck stubbornly to it: obscenely cheap phones running Google’s Android operating system. Its first strong budget phone, the ZMax, debuted for $200; and its successor, the ZMax 2, hit the street for $50 less ($150). That strategy proved to be a good one: Last year, ZTE sold more than 15 million handsets. Now it’s back with the $100 ZMax Pro.

But while a low sticker pr