we claimed a few years ago and Tesco were very helpful and paid the vet in full less a small excess. They have an advice line which is great too.
The downside is that for older cats the premium rises steeply (I know that statistically older cats are more likely to need the vets but it does go up a lot)to a point where we've decided to look elsewhere for cover.
In summary great for younger cats, not for older ones