I had state farm before, I bought a new car and sold the old, state farm was charging me 120$ a month for full coverage and that doesn't include broken windshield. I didn't think of getting a new insurance company had it not been for my state farm agent who kept on ignoring me. I kept on calling him but someone else is answering the phone, he takes my message and tells me my agent would call me back. He never did. I happen to drive by a geico office and decided to inquire. For the same full coverage I had with state farm plus the windshield insurance, they're charging me 90$/mo. That's 360$ savings a year! Plus they gave me some freebies like pens, tumbler and stuff like that. Went to AAA and they said they wont insure me cause my US license is less than 18 months old. They wouldn't Honor my professional drivers license from another country even if I'm 30 yo. Geico on the other hand gave me more discount because of that license and another discount for being a Registered nurse.
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.