The promise is more "we will deep freeze your brain, and in the future we will maybe come up with a technology that allows us to resurrect you in whatever form". Which is what companies like Alcor have been promising for decades already. So for people who sign up it's more like betting a sizeable amount of money on a small chance that they will be resurrected someday, which is still better (in their opinion at least) than dying like everyone else does...
