For those who read comments here first, I read the abstract, here's my tl;dr:
The people in developed countries who buy themselves things to save time are happier than those who don't.
Yup. Sounds about right.
The people in developed countries who buy themselves things to save time are happier than those who don't.
Yup. Sounds about right.
The people in developed countries who buy themselves things to save time are happier than those who instead buy material objects.
Maybe my definition is off but the fact these physically don't last long makes them seem less material.