They literally recommended Extend and Mulberry in the same email, which is the answer to your question.
Both are solid alternatives. Extend is the bigger player in shipping protection and product warranty, well established, integrates cleanly with Shopify, used by a lot of mid to large stores. Mulberry is the other main one, similar feature set, sometimes more flexible on customization and merchant terms. Worth getting demos from both and comparing the revenue share split since that’s usually where they differ most.