Thanks everyone for the replies! @Scott Skinger, @Hadar Orkibi, @Rod Khleif, @Omar Khan, @Gino Barbaro
I get the risk premium approach inherent in using cap rates (I'm an actuary at an investments firm :-) and using them for large MFHs, which are primarily investment vehicles.
And I get using comps for SFH - they are primarily not sold as investment vehicles.
Learning that 2-4 units (or maybe a bit larger) are generally valued using comps seems to set up the potential for market inefficiencies. Which are always intriguing...
One follow-up. In "What every real estate investor needs to know about cash flow..." Gallinelli talks about these smaller properties being valued using Gross Rent Multipliers as well as comps. While GRM is a type of comp, it's sort of a hybrid between an investment return measure like cap rates (since it at least considers income, though not expenses) and a strict comp measure like price per unit. Since no one has mentioned it, should I take it that those replying don't typically see GRM used in valuing small MFHs?
Thanks again, this is extremely helpful!