Fun Fact:  if you take a purely hypothetical 'break even' property at 100k with 20% down, where the rents equal the mortgage plus expenses, and assume that rents rise at the same level as inflation then after the first year your break even property will start to turn a small profit since rent went up, and while your expenses went up, they did not go up as fast because your biggest expense (debt service) stays constant. 

Returns will be much lower than other alternatives, but purely passive and likely less risk than the stock market.

It has never failed me yet but one must a bit careful with this stuff as it is pure lye (won't hurt pipes but it does smoke when boiling water is poured over it so don't breath the stuff in).Gail

There is a huge demand not only for owner occupied 2-4 units, aka house hack, but also there is demand for pure investors not looking to owner occupy.  2-4 units are a popular investment vehicle and is loudly touted from the roof tops in my circles, REIA groups and all over the web including here where the term house hacking was invented by @Brandon Turner, though I think I personally did house hacking before him, but didn't know the term.I have related in print previously about a friend of mine who bought, a condo, 3 townhouse, a 3 unit apartment, a 4 unit apartment building and a farm; all as an owner occupant. 

Combined, I'm seeing about $2k a month in pure cash flow.

You have a little more leeway with the numbers as a house hack rather than pure investment property.

Or is it a pure rental?

My purely anecdotal experience over the past...I don't know...6-12 months...is that there are a lot of multi-unit properties that are going on the market and then being taken off the market after 90-120 days. 

yelp review I'm mostly from the tenants. half of them are purely emotional but  half of them are pretty factual and leaving me with the feeling that my p.m. company Can turn a good tenant into bed Tenant.  

That limits the market to only pure investors, many of which who are looking for larger buildings.