(a) Notwithstanding any other law, a general property and casualty agent or a personal lines property and casualty agent who holds a license under Chapter 4051 may enter into a written agreement with a purchaser of insurance from the agent that provides for the payment of interest to the agent on any amount due to the agent for the insurance purchased. The interest is computed at a rate not to exceed the greater of:
(1) a rate allowed by Chapter 303, Finance Code; or
(2) the rate of one percent a month.
(b) A claim or defense of usury may not be raised in connection with a written agreement under this section.