Unless you have one of the Primary cards don’t forget your own insurance pays first and you will have to pay whatever deductible you carry for your insurance policy.
Something else to note. Although you may carry “Uninsured Motorists” insurance you will still have to come up with your “Deductible” for damage to your car if they can’t get it out of the other guy assuming it’s his fault.
Both might be good reasons to buy the Rental Waiver even though I hate it.