I like the look of them, but have never understood what people actually use them for.

Generally, they don't use them for anything. Kind of cyberpunk LARPing or something.

They actually have a purpose, if you're in a role where you need to interface with a lot electro-mechanical stuff of varying vintage though. Basically ends up being a pelican case with a fat battery, a small network with short patch cables for reconfiguration on the go, two SBCs running windows IOT and linux, a PLC + 2/3 I/O cards, a CAN adapter and some space for 6 inches of terminal block on a DIN rail. Then a keyboard + monitor.

Maybe not as sexy as some people make but it is a cyberdeck/briefcase lab and it will allow you probe most distressed machines without having to waste time running around for supplies or back and forth to offices.

The way many manufacturers are structured however, there is too much red-tape and osha for this to be a reality for a lot of people, at least in the usa. It does exist in some places though.

Speaking only for myself, I'd love to have a modern netbook with great battery life and a decent keyboard. I'd carry that around with me all the time to hack on random bits of code or whatever when the mood strikes.

If I weren't completely tired of waiting for iPadOS to grow a Terminal.app, an iPad mini with a keyboard folio case would be nearly my ideal portable computer. For functionality, I'd vastly prefer something in that form factor that only supported text mode of something that had a beautiful GUI but no terminal. At least I could run emacs and fish shell there, and that'd cover 98% of my on-the-go needs.

Super bonus points if you can make the thing look cool at the same time, but that's just icing on the cake.

My impression is, that movement it's more about having a modern accessory. All the videos I've seen so far are about look, not technology, purpose or actual usage; thus I label them fashion-deck. Kinda strange, but maybe something more will grow from this.

Yeah, it's a fun, retro aesthetic; but I also care about having computers on my person that are genuinely useful for things I want to do, just as my smartphone is useful.