The difficulty of hydrogen comes from it being difficult to store long term since it leaks so easily. It could be useful for heat at low pressures or as an engine fuel if infrastructure to pressurize it is available. The article didn’t mention if the device separated the oxygen from the hydrogen though. HHO gas is significantly more volatile and difficult to use.

Nighthawkinlight on YouTube has a few videos on the ways hydrogen gas and HHO need to be handled differently iirc.