“It’s opt-in, and it’s understood from the beginning what’s going on here,” Mr. Constable said. “That level of control is explicit: you can plug in and you can remove the information that’s there.

“It’s a very simple bargain — it’s, ‘You share with me, and I am going to make your life better.’ It’s not about privacy versus lack of privacy — it really does come down to control and giving people choice.”