I think the bit about putting some money aside each week or month for the cat/cats is the best one, as long as you do. I have worked out over the years that I have had cats, and that is over 30 years, that most of the things veterinary costs have been for, would probably come under the minimum amount you could claim for. Others sadly have been lost to the road, and a lot of things are not covered anyway. In rescue we obviously are dealing with pregnant females, and I doubt that would be covered.
Remember these companies are out there to make a profit. I think if you do your best, feed well, don't let out after dark and good management, i.e. if they miss a feed, don't panic and rush straight to the vet it could be something simple, but on the other hand if you think you can recognise a potential problem get it sorted sooner rather than later. One of my older foster youngsters came up with a lump on his neck on Sunday night, deep breath, thought about it, and realised it was his injection site! Had another injection 2nd kitten vax, and here we are again, lump has come up again. I know they will go down without calling the vet out on a Saturday night. If it has not improved by Monday then I may well call them about it.
Some people feel better knowing they are covered, but it can be costly, and annoying when you find the thing you thought was covered isn't.