Got all mine insured with Pet Plan, not the cheapest, but the only one my vet is happy to claim from direct, so apart from paying any excess, I dont have to pay upfront and claim money back. Never had any problems, and have made a few claims.
I used to be with DBI, they would only pay for any illness once in a dogs lifetime. Eg: one of my males had a few 'footballing injuries' and used to knock his claws back when skidding, after the first time they wouldnt pay for any veterinary treatment. They also asked me for a death certificate when I lost one due to old age and cancelled the premiums, which was heartless and unnecessary in the circumstances.
I dont mind paying insurance and not claiming, at least then I know my dogs are healthy and not requiring veterinary treatment, but I have the peace of mind that if they need expensive treatment, I have insurance backup.