I was a NFU agent for over 20 years and am still very supportive of the company. They aren't Brokers, you are dealing direct with a mutual company and, yes, rates can appear expensive at times. Then again, plenty of people are prepared to spend a lot more for what they perceive to be premium brands of cars, you tend to get what you pay for. My advice was always to deal with a well known Insurer, avoid the ones you haven't heard of before.
NFU has topped the Auto Express magazine survey of insurers for the past 4 years. From memory, SAGA also came out well.
People don't always realise differences in cover. Business use, hidden excesses, limits on windscreen cover, all important issues. Some companies deal with vehicle theft very differently to others, you don't need the worry if you are in that position.
When the claim comes, I know from experience where I want to be insured, you can deal with a local Office and, in general, no one will serve you better. It wasn't always perfect by any means, we had our problems, but used to hear some dreadful stories from time to time about other companies.
My insurance is due soon and I know there there have been increases so I'll probably be complaining also.