I'm glad you've got answers, and how awful that the insurance company don't support removing all that stress from him. I'm sorry you're going through this.
I've been using an all in one tick/flea/ wormer from the vets for the outdoor cats. Currently, due to various unfortunate things (regulation changes that mean they have must be seen within a year, vaccinations that mean you can go longer than a year, busy diaries) I am stuck with picking out...