Income restricted apartment for an investment

[Stephen Scire]

I am getting my children interested in real estate investing, my son has come across a 2 unit in a lower income area , suburb of Boston.

These 2 units are said to be  " deeded rent restrictions for low income occupants" ... these affordable housing restrictions are in place for the next 7 years. 

What are the benefits & pitfalls being a landlord owning an investment like this.