Charm co-founder here... We are not betting on hydrogen fuel cell cars. There is an existing $120B/year market for hydrogen used in the production of ammonia fertilizer and oil refining. That hydrogen is currently produced from fossil natural gas, and we are replacing that.
The Sleipner Project for geological carbon sequestration has been ongoing for 20 years with extremely rigorous measurement. We also know that natural gas is stored in geological deposits for millions of years, and in vast quantities. I don't see a strong reason to be skeptical of long-term sequestration a slightly different gas in those same geological formations.