It seems to be a "just add water" kind of reaction, (underscoring water's importance as the universal solvent/reagent on Earth,) and as far as I can see, produces no other byproducts. Quick, what's the catch?
Reading their site, one phrase that crops up is "...Carbon Sciences is developing a proprietary process that requires significantly less energy than other approaches that have been tried." which implies that there is still going to be an energy cost to the conversion. Also, they do specifically mention splitting water into H and OH, a process which inevitably requires energy.
On the plus side, as long as supplying that energy requirement produces less carbon emissions than the original amount of CO2 being converted, we're ahead - the amount of CO2 will eventually diminish.
Also, providing much of the needed energy from some source like sunlight would be even better. Since a catalyst is involved, that means that the reaction needs little in the way of resources once the initial "working capital" of catalyst is acquired, and water is thankfully still plentiful enough.
One further thought, and this is a wild stab in the dark - but if the process could use partially treated sewage water, and the process returned a certain quantity of recombined H2O at the end, then that would be even better. (If you split water into H and OH, that effectively leaves all other material behind. Recombining it into H2O again therefore produces totally pure potable water.)
Last observation: Using propane gas for running vehicles results in cleaner operation than using liquid fuels, and most car engines can be converted. So there's a further saving: the fuel produced by this reaction is cleaner to use.