Why is Geico so much cheaper than Farmers for car insurance?

I’ve been with Farmers for a few years, but my last renewal quote jumped significantly. I decided to shop around and got a quote from Geico that’s drastically lower. For what seems like the same coverage, Farmers wants $875 for a 6-month term, while Geico quoted me only $479 for the same period. That’s a difference of almost $400 every six months! I also got a Progressive quote for $679. While I like having a local Farmers agent, the savings with Geico are tempting. For those who have experience with either company, especially considering this big price gap, what are the potential downsides of switching to Geico that I should be aware of?