Feedback from beta readers has proved useful for me, helping to pick out inconsistencies. This is partly because I chose people who I know are observant and not afraid of speaking their mind—much like me—but being objective about my writing is impossible. I can tell if it works in regard to the spelling, punctuation and formatting, but does it work as a story?
Quite inadvertently, I also chose three readers who weren't big fans of my genre of crime fiction. All have gone on to read more crime novels. It made me realise how close-minded many people are, as well as how restrictive it is to have to write a book that conforms to the expected norms of a genre. We all have preconceptions: simply think how differently you'd react to strangers telling you they wrote romance or science-fiction.
It made me wonder afterwards, if it was better to choose readers who don't normally tackle my genre. Giving my novel to someone who only read crime fiction would inevitably lead to comparisons, whereas an inexperienced reader would offer an unbiased opinion.
As a bonus, one of my readers came up with a brilliant plot twist for a scene in which a burglar was surprised rummaging through the contents of a storage chest. I'd been so focused on getting the technical details of the consequent gunfight correct, that I'd missed an opportunity. I welcomed the suggestion, as I don't really have an ego when asking for assistance.
I'd find it more worrying if beta readers approved of everything I'd written.