I bought ASPCA for an 8 year old golden retriever when I first adopted her, and the premium was reasonable $25 per month. When she turned 10, they increased it to $45 a month. I thought that having a prior relationship with them would mean they wouldn't overcharge just as my pet ages.
Also, the policy can vary from state to state. I adopted my dog in Montana, but currently live in Oregon. I just found out that due to policy changes in Oregon, my dog is no longer eligible for ASPCA insurance. Oregon's rules essentially require that ASPCA insured dogs have the "extended care option". I would enroll my dog in it, but they will not enroll any dogs over age 8. I'm pretty ticked off that ASPCA is essentially kicking my dog off of their plan just because she aged, and that now I'm having to search for new insurance plans and enroll a 10 year old. (It's insanely expensive).
When I did submit claims, they were generally accepted and reimbursed promptly. In this regard, ASPCA was better than my human health insurance. Claims I submitted were fairly minor and included a hurt paw, eye infection, and metabolic panel.