Glenn (and Popular Mechanics) confuse the terms. As is pointed out in the article, rocket packs aren’t “jet” packs.

Remember the rules? If you want to cruise in the atmosphere, use an air breather. A rocket belt sounds cool, but it really makes no sense for this application. Rockets are for accelerating, and getting out of the atmosphere as soon as possible (or for traveling in space, if you’ve already done that). They’re not for tooling around near the ground, or for atmospheric transportation (rocket races being an exception, because it helps push the technology, and sounds cool). A true jet pack, though, would be actually cool, as opposed to merely sounding (and looking, when you see a pro do it at a show, for a minute or so) cool.