Tried it and the lowest priced company it showed had a rate that was ~$250 cheaper than the actual quote I could get on the insurers web site. Plus my current company (Safeco) wasn't in the comparison list, which means the cheapest company (for me) isn't shown.
Not being in the US I'm not going to try it, but does this not work like the UK ones, where that's a real actual price and you click straight through to buying with the company at that quote?
--EDIT-- no I see that it does not work like this, now that I've read more about it, it predicts rates. Here's hoping they can actually integrate with insurers in future because the services like that here in the UK are pretty useful.
Try EZquo.com to get a quote from any company, including Safeco and the other carriers rated best on price and customer satisfaction by J.D. Power. It's a simple website that I built over the last few months: you enter your insurance details and get a private link that you can pass to any agent for a quote, without having to repeat your information.