How does Coinbase primes charge a fee?

Could you elaborate on the fee structure of Coinbase Primes? I'm particularly interested in understanding how they charge for their services. Do they have a flat monthly fee? Are there transaction-based charges? Are there any hidden costs or additional fees that clients should be aware of? Additionally, how do their fees compare to other similar platforms in the cryptocurrency and finance industry? Clarifying these points would help me make an informed decision about whether Coinbase Primes is the right fit for my financial needs.