He strongly discouraged adding a backwater preventer bc he said he's seen it make things worse.

But, they will be in challenging parts of town where realistically you do not want to own property and your long-run returns will under-perform.I'd encourage you to find a balance of sub-market growth, nearby employment, strong income, and only then a good rent-to-value ratio. 

Another important thing to keep in mind is that markets with strong cashflow won't typically have as much appreciation.

The cons as i see it include loosing the 2 of 5 year cap gain exception, typically not an ideal rental because the emphasis at purchase was buying a good home for your family and not a rental with optimal return (my ex-home consistently has the lowest cash flow for equity in my RE portfolio), not disconnected enough from the property causes addition angst on damage and may result in over improvement.  

Sharon, thanks for sharing these stats—Houston is clearly holding strong!

Focus on affordable markets, build a strong network, and continually educate yourself through books, podcasts, and deal analysis to steadily expand your portfolio.Good luck!

Some rents in what some define as an A may hold strong values but rents compared to purchase price may not be comparable to a B.

i strongly disagree with this. 

It is entirely possible to self-manage with a strong cleaning team.

Boston in particular is a strong market with great appreciation, a great tenant pool, and rents being as insane as they are it's nearly impossible not to pay less when you house hack vs. rent.