The determination by the governing body of any public body issuing refunding bonds under this article that the limitations herein imposed upon the issuance of refunding bonds have been met, shall be conclusive: Provided, however, That such public body shall have obtained from an independent certified public accountant a certification that the amount of saving stated to be achieved by the refunding shall in fact be served, based upon his review, comparison and analysis of the net interest cost in dollars of the refunding bonds and the net interest cost in dollars of the bonds to be refunded.