Hello Pierre:
My take is the short intermittency cycle of kite-reeling is not suitable for such a longer-cycle-time solution as this CO2 turbine idea. Probably a battery or even capacitors would be more suitable. The CO2 solution, if it actually works as an economical energy solution, would be better suited to address longer-cycle intermittency, such as generating power after the daily wind stops blowing.
I was also initially intrigued when I read about the CO2 cycle energy storage idea. But then, I thought about it just a bit, and realized we had not seen any of the little details which might present problems with this idea. If all we see is the press-release, all we are exposed to is a possibly over-optimistic treatment of an idea that may have fatal flaws for all we know.
I would caution anyone reading any of these online “science” magazine “press-release breakthroughs” to generally be skeptical, as these articles are mostly click-bait, and do not present a sufficiently round view of the story to properly analyze it. Instead, these articles are like free advertisements for the promoters of these often unworkable ideas.
For reference, think about all those articles from a couple of years ago, about cranes lifting concrete blocks into stacks for energy storage. What ever happened to that? Any follow-thru on the development of that silly idea? Someone finally did some math on the back of an envelope and figured out it was not a workable solution?
Anyway, back to hydrogen: It seems that it is often combined with other stupid ideas. For example, if some idiot wants to promote a bad, unworkable and uneconomical wind energy idea, their instinct is often to “combine” it (on paper only, of course) with “hydrogen production”. How many times have you heard that in the last few years? Whacky offshore wind turbine ideas, always claiming they can be combined with electrolyzers, to produce hydrogen(!) Wheeee! We’re on a roll now!
The idea is, if they can make the story complicated enough, they can avoid any direct comparison of, let’s say, their wind energy idea, to existing wind turbines. That way they can just keep pretending, with their more complicated scenario, that it could ever pan out as an economic energy solution. No, throwing away 75% of your energy is NOT a good storage solution. It is a bad idea. Period. The people promoting it are… idiots. 
As far as compressed air as an energy storage solution, the idea has been around forever. Maybe ten years ago, we were treated to soon-to-be-popular compressed-air-powered cars. I think one main company was in France. So, after all these years, where is a single compressed-air energy storage system? What it amounts to is an old adage: “A little bit of knowledge is a dangerous thing.” As long as we only hear one side of a story, we are easily convinced. We need to step back and look at the whole picture. The problem is, the whole story usually won’t fit on a bumper-sticker.