Unless prohibited or otherwise limited by the instrument under which a fiduciary is acting, including a fiduciary of an agency account, the fiduciary may invest in a mutual company, investment trust, or investment company sponsored, advised, or sold by the fiduciary or an affiliate if the investment is otherwise appropriate as an investment. In such case, the fiduciary shall not take a commission as fiduciary to the extent that the fiduciary, or its affiliate or division, receive compensation for services relating to advice or services to such mutual fund, investment trust, or investment company, unless (i) otherwise expressly agreed in writing by the creator of the trust or affected beneficiary or (ii) the fiduciary discloses by statement, prospectus, or otherwise to all current income beneficiaries of an account the rate, formula, or other method by which the compensation received or to be received by the fiduciary or affiliate or division of the fiduciary for such advice and services is determined. In such case, the compensation for such advice and services shall not exceed the customary or prevailing amount that is charged by a fiduciary, or its affiliate or division, for providing comparable advice and services for the benefit of nonfiduciary accounts.