I just saved about $400 dollars a year by switching to AAA from State Farm. The coverage for my cars is the same and the coverage for my home is much better (and cheaper) than before. I have a credit card through AAA, roadside assistance through AAA and finally, my insurance through AAA. I could not be happier. On all fronts, AAA has the best customer service I've ever encountered.
The underinsured motorist coverage works similarly, but it would only pay out when you get hit by someone who does have auto insurance, but your bodily injury damages that they caused are more than they carry, leaving them underinsured. Just like your bodily injury, the UMPD would pay to fix the damage to your car caused by the other driver, and you only have to pay the $250 deductible.
Best kept secret in auto insurance. The people are friendly and genuine, very helpful. Grange does not raise your rates just because a deer jumps in front of your brand new car four months after signing up. An insurance company that sticks with me after paying my $8,300 auto body repair bill without raising my rates has earned my business and my trust for a long time!