How smooth is the claim process and reimbursement for insurance companies such as Aviva and Prudential?

If you satisfy the conditions for your claim to be admissible, you will get paid promtly. Else, your claim will not go through. It's a very fair system. If you think you have not been treated fairly, you can always appeal. You can also bring your case up for dispute resolution with FIDREC, who will give you a fair hearing.