Microsoft's pricey Surface Book is getting stomped by the ancient Surface Pro 3

Though deciding between the Surface Book and the Surface Pro 4 was an agonizing choice for PCWorld editors, customers apparently know what they want: The Surface Pro 3—yes, the older one.
AdDuplex, a Windows-specific ad network which compiles data on Windows machines, estimates that an even third of all Surface users are using a Surface Pro 3, a convertible tablet Microsoft phased out when its successor, the Surface Pro 4, began shipping in late 2015. SP4 sales are closing fast, though: A