These insurances vary a lot in the small print and all should be read carefully. some exclude dogs above a certain age, or certain breeds above a certain age, some require the illness or injury to be reported to them within 48 hours of it happening or being first noticed, some have long lists of excluded conditions, some demand substantial payment like an excess in motor insurance, and so on.
All of them cost a lot for cover which is properly useful; I am not impressed by £10 million public liability against £5 million, as one firm touted as a benefit, when that firm has ridiculous restrictions on other matters !