Based on the pretty good reviews here I was about to give PetFirst a try but thankfully read their exclusions prior to signing up. The most concerning exclusion is the second-to-last in their list and reads as follows:
"Continuous coverage of chronic and long term conditions that manifest in a previous policy year".
Which I understand to mean that if your pet were unlucky enough to be diagnosed with a chronic or long-term illness at the end of your policy year, this illness will not be covered anymore, even if you renewed your policy for another year.
I'd say: Buyer beware, because these kinds of illnesses are usually the ones that are the most costly and to discover that you do not have coverage for these anymore because your policy is up for renewal - I don't know. Sounds like a raw deal to me.