Even after one year, that property may provide thousands of dollars worth of appreciation, you will pay down your loan and build some equity, and you can depreciate the asset. 

Any underrated markets worth exploring?

I think it’s definitely worth looking into.

If you pay off a property or owe more than it’s worth, you can still owe or not owe capital gains tax.

How much is the property worth?

Also, for what it's worth, just because someone is in the military doesn't mean he isn't a bum.

You already have a pretty solid portfolio, so adding another property and generating more cash flow might accelerate your wealth in a way that the Roth can’t match, especially if you’re planning to transition to real estate full-time soon.The long-term game for you seems to be building that cash flow and equity in real estate, and it sounds like taking the hit on the Roth 401(k) could be worth it for the immediate returns.

The biggest pro, is typically you will have a higher rental rate, if your home is already furnished and you have no place or desire to store it, it might be worth it. 

however, if you could find a loan product that worked for you and your situation, its a fantastic idea in my mind, and worth taking a swing for.

I will say though if this is your only option and you're confident in finding a deal below market value, then it might be worth it.