No group annuity contract shall be delivered or issued for delivery in this state and no certificate shall be used in connection therewith unless it contains in substance the provisions set forth in sections twenty-three to twenty-seven, inclusive, of this article, to the extent that such provisions are applicable to such contract or to such certificate, as the case may be, or provisions which in the opinion of the commissioner are more favorable to annuitants, or not less favorable to annuitants and more favorable to the holders.
