Just to note, the linked story is about David Mayman of Jetpack Aviation in California, while the other stories you mentioned are (British) Richard Browning of Gravity Industries - the one recognisable by its wrist-mounted supplementary engines. So there are at least a couple of competing inventions.

Sure, there isn't a killer app for jet packs at the moment, or perhaps ever. They were enabled by miniature-scale turbine engines being developed for other purposes. But you never know - some innovation in control systems, or them turning out to be just perfect for some obscure emergency/military task, they might find a niche beyond stunts and tethered tourist experiences.