That was my thought too reading the OP. I'd pay the $400 out of pocket now and investigate insurance later, always keeping in mind the balance between the cost of insurance and paying your own way, maybe putting aside the cost of premiums in a separate savings account if you're the kind with enough self-discipline to do that.
Where you come out on pet insurance is when you have the really big bills - orthopedic surgery, cancer treatment, etc., and the insurance company can't deny the treatment was necessary. My single experience with insurance was that even then, it's not like they pay all costs. They're just like human health insurers in that some things aren't covered at all and for those that are they only cover a percentage. So - $3,000 TPLO (cruciate repair) surgery - first they claim it should only cost $2,000 and then they only pay 80% of that. Better than nothing, but not what you're expecting. Since I canceled the policy not long after, I did come out decently ahead financially balancing what I paid out in premiums against what I received.
Also, I once talked to a woman whose dog only survived kidney failure because the insurance company paid the cost of regular dialysis for months. The dog did eventually recover kidney function. So there was someone whose dog only lived because she had the insurance (no way she could have paid for the treatment herself).
