As I understand it:

1. You don't have to worry about personal injury insurance; all States have
such insurance included as part of the car's registration. (CTP = compulsory
third party insurance; all registered vehicles are so covered). You can't
even buy such insurance excepting as part of registering a vehicle.

2. Most car rental places already include some form of damage insurance, its
just that these typically have quite high excesses (eg you pay the first
$2,000 on any claim). In this case, you are really only insuring the excess.
If they don't explain this on their web pages, I am sure you could ring them
and ask them. This is called "CDW" or collision damage waiver insurance,
though it covers theft etc as well.

3. All rental car insurance is a rip-off, and those policies offered at the
point-of-sale by the car rental company are a massive rip-off.

4. If you rent a car using an Amex credit card, its quite possible that you
will get free CDW through Amex (which shows you what a rip-off this
insurance is, that Amex gives it away free).

5. If you can't get free CDW insurance through Amex, my suggestion would be
to find a car rental company with a reasonable excess, and simply don't
bother.