When I was younger I used to always get pitched on MLM and because I was younger I did a number of them. I was definitely not cut out for MLM but it was very interesting to see how some people just crushed it and others fell flat. I think it boiled down to either having natural talent or working really hard and being able to switch up when something didn't work.
I think of lower income properties in much the same manner. They have a bad rep and require a lot of work but you will always meet some people who made a killing.
That inherent ability to do really well with these boils down to two things in my opinion. First, the cash flow (if you can actually capture it) can be great. This is even more true if is section 8, where the rents are inflated normally by being benchmarked to some metric that includes higher rent properties but where the property prices to buy are still depressed because well its not a great area.
Second, at least if you buy the right bad area it can go up as the area improves. True that might take a long time or never happen but as long as you are not banking on it at least there is real potential there. This is probably a lot more true in urban areas like Chicago, NYC, Oakland etc. etc. where there is a huge huge difference between nice areas and bad so people start moving into bad areas over time.
With that being said, like MLM, most people will probably not do well and a select few will. There a ton of pitfalls that can just crush you. from bad tenants from hell to city regulations that are impossible to figure out to taxes to bad rehab jobs etc. It is just a minefield. Its definitely not something that in my opinion you can just buy and sit back watching the good times roll.
By far once you buy the property (and buying the right property on the right block with the right rehab is very important) the most important thing is your property manager. These are about as management intensive as you can get. Most of your tenants don't care about their credit score, can't afford to give you a big deposit and will be really hard on the property. So you have very little leverage. Most are also fairly mobile and are one problem away from literally not being able to make rent. This is all assuming you have a generally well-intentioned tenant. If you have a tenant who knows the system and wants to play you, they will. It will happen eventually and if you only have one or two properties it can be a huge problem.
Further even the best property manager probably won't take care of the property like you can because they are there to follow the rules and do a certain amount of work in exchange for a percentage. it is rare that they can or will be able to do certain things that really matter to the success of the property.
As an example, I had a tenant that fell way behind on rent. Even once she started paying I had to call her every 30 days and she waited until the last day to pay every single month. My property manager wanted to kick her out and told her she had to pay or leave. Based on my interactions with her, including why she was late and the fact that she paid her last balance the day she got her tax refund I let her stay and talked to her about what I expected for doing so. She ended up staying until I got rid of the property and even paid me my late rent when she really probably didn't have to because what could I really do to her at that point?
She also thanked me profusely for taking a chance on her.
Course flip side she also called me every time she had a problem with anything and I sweating every month about my rent money.
In short, I think it can work but it requires skill (or learned skill) and a good amount of work. It also requires you do the work upfront to not buy on a bad block or a bad rehab (like the MI properties @Jay Hinrichs was talking about). Its definitely not easy.