MSRB Rule G-19 is the rough equivalent of FINRA Rule 2111, requiring that a broker-dealer recommending a transaction or strategy in regard to a municipal security have a reasonable basis to believe that the recommendation is suitable for the customer. Both rules have interpretations that go to a "product" consideration, a consideration of the customer, and a consideration of the product. While the specific wording of the rules and regulatory interpretations do vary, it is not clear how much, if any, significance that variation would have in practice. However, the two rules do provide for somewhat distinct exemptions. MSRB Rule G-19 provides a conditional exemption for transactions executed for "sophisticated municipal market professionals" (see MSRB Rule G-48), while the FINRA Rule provides a conditional exemption for transactions executed for "institutional accounts" (see FINRA Rule 4512(c)).
See also the topic page on Regulation Best Interest.