Paying off Student Loan vs. REI

[Roy C.]

Hello guys. I know this question has been asked many times before, but since every situation is different, I want to hear your feedback on my situation. 

I currently have $30k student debt. I have a very stable job with consistent income. Recently, I got enough money saved to cover this debt.  However, I am thinking about investing in a duplex instead of paying off my student debt. My reason is following:

I am currently living in an apartment, which I pay $600 a month on a rent. If I buy a duplex that costs around $150k, I have enough money to put down 20% down payment (and yes I am considering extra cost such as closing fee, inspection fee, etc). My student debt has 4% interest rate, and according to my calculation, I would have to pay about $6500 for interest in the end (in 10 year duration).  Now since i am paying $600 a month on rent, if i buy a duplex, it will go toward mortgage instead of giving away to someone else. So in theory, I am saving $600 a month on rent and putting it toward my asset. And since I am planning to buy a duplex, I will be renting 2 out 3 rooms to tenants, which will generate cash flow. So base on my crude math, I will be making $200-300 a month from tenant after taking care of extra cost. 

I personally feel like this sounds too good to be true. Yes, I do have an option to pay off my debt. But if I risk a little bit, it would benefit me tremendously in a long term according to my calculation. Did I miss something here? Did I forget to include in my decision (beside the fact that bad tenants can be a nightmare)? What do you guys think?