I have a mate who had critical illness cover. He's one of the very pale-skinned, ginger haired types (except he's lost what ginger hair he did have).
He got diagnosed with skin cancer. Had the surgery, chemo, radio etc. Critical Illness cover paid up. Paid off his mortgage. And he survived the cancer, so ok he has a scar on his arm, but he has no mortgage. Lucky man.
I'd say think about it if there's a history of say cancer in the family, or you're a pale-skinned ginger-haired sun-worshipper…