I see one big drawback:
You have to use pretty much all the fuel in your tank, or you're wasting fuel. If you have "a quarter of a tank", as it were, while driving past the last filling station for 100 miles, you'd better dump what good fuel you have and fill up.
That could be a big cost/efficiency issue.

@Anne Ominous: we've asked for clarification on this. My initial understanding is that a range of different tank designs will be available, some of which may include the addition of a spent fuel tank to keep fresh and spent fuel separate.

I totally agree with Anne Ominous' point. Also the fact that you are essentially paying for transporting the 'carrier fuel' in fuel consumption. So at a guess, you would be permanently carrying the equivalent of one extra, large passenger, all the time. I understand that is the same as any other fossil fuel but 1. You get to use all that fuel, 2. This factor seriously negates the 'Eco value' of this new wonder fuel. For example, the added carbon cost of transporting the spent fuel to be reprocessed.
The MASSIVE difference between this fuel and batteries/hydrogen is that the latter fuel sources do not need to be transported back and forth using additional transport. There are hydrogen generators that can be installed at fuel stations, instead of it being shipped there in cryotankers. Electricity should also be generated at (or very near) the pump, using wind/solar/hydro. Or indeed at the car owners own houses or a turbine per number of streets.
I am still amazed that Tesla never took the initiative on this and installed generation systems on-site for their superchargers.

Between transportation and conversion losses it doesn't seem to have an overall efficiency higher than conventional fuels. As well as, the current limiting step of H2 use is in the fuel cells cost, which is still there.

"Does the Switch catalyst need to be refilled?" "Yes," says Simonetti, "like a filter on a car. Once a year, or whatever it ends up being."
Well, this is the point, one can realize, it's just a hoax.
If the "catalist" have to be "refilled" regularly, then it is not "catalist", but it's just the fuel itself.
The "catalist" can be any water-decomposing, hidrogen-generating light metal or alloy, like lithium, sodium or aluminum.
And the only "invetion" is just how can you get some investment a live life in prosperity, while "developing" a hoax.

@Anne: I think that can be easily surmounted by using multiple slots to store fuel and deplete them one after another.

Hydrogen fuel cells have not been mainstream owing in part, to their degeneration from impurities in the hydrogen, otherwise called "poisoning'. What has been done about this? Do the fuel cells need to be regularly replaced and if so at what cost and inconvenience? Lastly, the production of hydrogen itself although simple, is extremely energy inefficient although with renewable energy this is somewhat mitigated. Interesting technology and worth watching how the Chinese company fares with it's vehicles.

A paper on the current state of fuel cells and their problems and promises. I would love for hydrogen fuel cells to become the standard but the technology has for decades had some intractable problems. This link describes the issues. https://reader.elsevier.com/reader/sd/pii/S2095809917307750?token=71838B081FD0674776193B5391E8FC7B9617A53D8C43B090B9E51A2BFD56909FE2D8F90E88A55F386F6505B83D65DC9E

It seems like this could also be a viable possibility for grid storage of renewable electricity.

The main drawback to this is that they're keeping it proprietary. In doing this, they hope to replace the stranglehold currently imposed by the "evil" fossil-fuel companies with their own. If you really want to change the world with your "miracle" H2 cure, then open it up... release the tech to the world and don't try to keep your hooks in it. Only then will this be of any benefit to mankind.