HYMB vs MFLX

HYMBAState Street SPDR Nuveen ICE High Yield Municipal Bond ETF

MFLXCFirst Trust Flexible Municipal High Income ETF

In short

HYMB Most muni index funds stop at investment grade. HYMB keeps going: its benchmark reaches from A-rated paper down through unrated deals, spreading roughly 1,900 tax-exempt bonds across that credit line. Income lands monthly.

MFLX Launched in 2016 as a basket of closed-end muni funds, MFLX was rebuilt in 2022 into a hands-on portfolio of roughly 80 high-yield munis, with closed-end-style leverage available through tender option bond trusts.

Stated mandate

HYMB The fund seeks to track, before fees and expenses, the price and yield performance of the ICE US Select High Yield Crossover Municipal Index, which covers lower-rated and unrated tax-exempt municipal debt issued in the United States.

MFLX The Fund seeks current income by investing at least 80% of its net assets in municipal debt securities whose interest is exempt from regular federal income taxes.

Why people hold it

• HYMB The crossover mandate is the whole point: the index covers lower-rated (A3/A+ or lower) and unrated tax-exempt debt, not another top-grade general-obligation ladder.ssga.com
• About 1,900 bonds dilute any single issuer's trouble, and State Street has run the fund since 2011, through more than one muni credit scare.
• One of the more actively traded funds in the muni ETF aisle, which counts in a market where the underlying bonds themselves can sit still for weeks. Pays monthly.

• MFLX Go-anywhere active mandate: any maturity, duration or credit quality, with a stated tilt toward longer, higher-yielding bonds rated below investment grade or unrated.sec.gov
• The 80% federally tax-exempt policy is fundamental, meaning First Trust cannot change it without a shareholder vote.ftportfolios.com
• A roughly 80-bond portfolio that pays monthly, concentrated enough that individual credit calls move the needle.
• Can borrow through tender option bond trusts and hold the inverse floaters: closed-end-fund plumbing inside an ETF wrapper.sec.gov

Worth knowing

• HYMB 0.35% a year is the toll for assembling illiquid paper. Broad, plain-vanilla muni index funds such as VTEB and SCMB charge 0.03%.
• Lower-rated and unrated munis carry default and downgrade risk that top-rated general-obligation bonds don't, and prices can move sharply when muni buyers step back.
• The benchmark has been swapped before (Bloomberg to ICE in 2025), so older track records reflect a different index than the one the fund follows now.ssga.com

• MFLX At 0.49%, it charges above the category median of 19 funds, and above index-based peers HYD (0.32%) and HYMB (0.35%).
• Leverage plus a long-duration, lower-rated tilt cuts both ways: price swings can run sharper than a plain investment-grade muni fund's.sec.gov
• It stays small and trades lightly, so spreads can be wider than in the category's heavyweights.

Full HYMB profile⁠

Full MFLX profile⁠