If 10 shares are not reached within 12 hours, the prism (zap split) is created.
Yes, it's a matter of trust. The idea of prisms is good, but it doesn't have a smart contract, which would allow the creator to block payment.
Unfortunately, there are people who use boosts in a fraudulent way. Some don't pay, and it's likely that there are bots finding prisms. On noStrudel, when zaping a prism, it's still possible to choose who gets paid.