The issue for small landlords, especially single unit is the concentration of risk. Let’s say you run the numbers against a $100k investment and it looks like the cash return (after debt service, management fees, repair and maintenance, insurance and property tax) plus property appreciation come out as a attractive numbers. All it takes is 1 bad tenant (or no tenant), 1 unanticipated casualty, some major plumbing, electrical, HVAC repair or replacement to wipe out your returns. If you are looking at retirement investments, you should be looking to reduce risk, not concentrate it.
If you are wanting a fixed and low risk stream of income and you want to hedge against changing interest rates, if you have enough money, you should look at laddering treasuries or other highly rated corporate bonds with different maturities. You basically can reset the overall effective interest rate in your fixed income portfolio each time one rung matures. Muni’s work if the after tax income works in your favor (you have high federal, state and local taxes in general). More than likely you will need an FA to help you with the ladder.