Indeed, the California Department of Consumer Affairs states pretty much the same thing on its page concerning postdated checks:
"The presentation of a postdated check is not subject to the civil or penal sanctions" that would normally apply to someone who wrote a check with insufficient funds because the postdated check promises "to discharge a present obligation at a future date" and that money would be available to meet the debt when the check is cashed.
Very generally a post dated check is not worth much as collateral for your loan. The borrower can clean out the account before the payment becomes due leaving you without the money and in basically the same position as if you had not taken anything to try to secure the loan as you are left with suing to collect your money. If you want security, get something as collateral that has value in and of itself and is not dependent on the borrower putting funds in an account later on.
