That's probably why Hertz does longer leases instead of rentals for this program. It would probably be worth it if you got it from locations outside of urban centers, but drove in the urban centers.
One "savings" I see is that you wouldn't have to wash your car (which in the city for me meant an extra $35 a week). You also save on general car maintenance. The city streets are tough on the suspension and brakes. You can drive that rental into the ground :)