Chris Coles
It opens the door to a revolution based upon the first demonstration . . . which always has to be further developed. Nice one, particularly as safety is the primary problem with hydrogen gas.
Bob Stuart
That's an excellent list of questions, Loz. I'm also curious about how they compare to the similar data on using methane to power fuel cells.
Bob Stuart: Problem with using methane is you get CO2 as a waste product along with water
You could ignore the inefficiencies if this goo is used for flight applications,especially if sourced from renewable energy. It could finally make carbon free flight practical. Certainly easier than using cryogenic H2 as a fuel. For powering land vehicles,it might bring fuel cell cars back from the brink,but efficiencies would come to the fore,especially when compared with batteries.
Expanded Viewpoint
FINALLY!!! An article about "clean" energy that asks at least a few of the more important (and often very embarrassing) questions about the veracity of the claims being made! ALL of the precursors of the process being touted as a game changer or some kind of panacea must be examined and factored into the equation. There is no room for the "and then some magic happens" in these equations.
The mining and processing of dirt to extract Magnesium is very energy intensive, and there's no way to get around that. All of the other chemicals and machinery and energy that is used in the process must be accounted for as well. Any time that we step outside of Nature and natural processes, costs are incurred, costs which cannot be ignored. If they are ignored, then we do so at our own peril.
Wind energy was supposed to be some kind of salvation for us, but when we add up all of the costs involved there, it's more of a curse than anything else! The same way with nuclear power, the costs which are kept hidden from our view far outweigh any benefits claimed to be present.

Bruce H. Anderson
From my experience in food processing, pumping a paste vs. pumping a liquid are two very different things. "Standard filling lines" and "relatively inexpensive equipment" sounds like wishful thinking.
While touting the positives against fossil and evs, what's the downsides to this pasty concoction? It's never picture perfect. If this paste reacts to water, what happens during a spill when it comes into contact with water? What's the MSDS facts?
I'm imagining a vehicle accident, during a rain storm, that manages to tear open the fuel tank. Exposed paste, with water from rain, and a spark from the accident. How easy will it be to put out a hydrogen fire? Water from a fire truck won't help.
A solar farm can be used to generate clean heat, and part of that heat could be use to generate the necessary pressure. And if the magnesium leftover can be recycled, it could avoid a lot of the cost and dirtiness of mining it. The transport could (should!) use hydrogen as well. So, while those questions do need to be answered, it could still be much cleaner than gas/petrol.
Moreover, even if the industrial process is not really clean, by concentrating in one place (the plant), it's much easier to capture the nasty by-products. (This is one of the argument that electric cars are better that ICE even if the electricity comes from coal plants)

The question about the magnesium after the process is quite an important too. Pure magnesium is not really safe (highly flammable). So if that's the leftover from extracting the hydrogen, we would just be moving the danger from the fuel side to the by-product side.
And in "large" enough quantity, magnesium is harmful to health as well. So how much of the magnesium would leak in the atmosphere?
“offering hydrogen fuel cell vehicles the ability to travel further than gasoline-powered ones, and refuel in minutes.”

Mighty lofty claims, lacking answers to Loz’s excellent questions.

It is not clear how they render magnesium hydride safe. Normally, it is violently reactive with water.