It can be costly, yes. But if you find the right plan with the right coverage you could get pretty good reimbursement for emergencies - or serious illnesses (like cancer). Which, really, emergencies or serious illness/injury would probably be what you use it for the most right?
We have it for Limerick and Dublin. We use Pet's Best and so far they've been great, fast with reimbursements, easy to work with. Dublin is around $62/month and Limerick is around $51/month. $500 deductible with 90% reimbursement. We chose one of the lower tier plans, but it still covers a good bit - exam fees, diagnostics (x-ray, ultrasound, blood, etc), specialty/specialists, surgeries, illness/injury, emergency. Even covers hereditary issues and cancer. The higher tier plans cover things like holistic care, rehab, alternative practices, and so on. Lower tier removes a few things (like the exam fees). We also opted to get their Wellness plan, which offers anywhere from $300-$450 or so reimbursement for preventative care (wellness exams, heart worm testing, flea/tick meds, and so on.)
We wish we had gotten Kiley insurance before they found her lung tumor. In the last year of her life we were at the vet every other month, or so it seemed - often enough to have easily met the deductible, at any rate. Could have saved a good couple thousand dollars but we don't regret paying it all. Just, now we know for future dogs.
The only downside is many insurances won't cover pre-existing conditions and will reach out to vets for records. So it won't really help if your dog has been to the vet for something you want covered. Some won't cover hereditary issues, some charge WAAAY more for mutts than purebreds, and some do increase their price drastically over time. If it's something you want to get for your pet/s, i suggest making a chart with a list of all the options. Write out the cost of each, if the prices increase over time (and how much), what each covers, doesn't cover, and so on.
I personally feel like it's worth it, but some people won't.