We have all our pets (2 dogs, 3 cats) insured with pet plan, we have never had any problems and they have never declined a claim, in fact our vet swears they are the only company that doesn't put him through administrative hoops on a claim. The vet fills in the form and gets paid and we pay whatever the excess is to him.
My border collie Ben needed a pacemaker and spinal surgery and cost was astronomical but petplan came through and took a lot of the stress and worry away, I don't have any knowledge about how good other insurers may be but I don't believe we will be changing from PP anytime soon.
Jim.