I've had Trupanion for 2.5 years, ever since getting my dog. I chose a high deductible on purpose. I wanted something that would be good if something catastrophic occurred but would also be good if she developed a chronic condition over time. The customer service person was very helpful. The monthly premiums have been reasonable, with minimal increases over time.
I have had no need to submit anything until the last few months. The first time, she did something to the point where she was unable to jump up. The total bill was under my deductible, so nothing paid. But a couple of weeks ago she went from being healthy to not eating, throwing up, and diarrhea that lasted over 24 hours. Of course, this was on the weekend. So off to the ER we went. She needed to stay overnight. But Trupanion covered everything they said they would. I met my deducible and they paid 90% of everything over it that they cover (does not cover initial exam). Claim submission is easy (upload a PDF of the bill). It took a week for them to process the claim. The money was deposited to my account within one business day of their emailing me their decision.
Needless to say, I'm very happy with them. They are different than your typical health insurance setup and I do recommend you read their materials thoroughly, so you understand that. I'm glad I did.