Here is one thread about it.https://www.biggerpockets.com/...Since its a conforming loan, there is little "risk" to it nor extra fees to my knowledge. 

Or even if you had extra money lying around, basically you’re planning a flip, which is rarely worthwhile for the first house (or few) anyone does.

What if I have some extra passive income that could pay the extra $2,140?

The only thing that would be better would be getting the FHA on a value add property, use the extra funds for a rehab, and then refi into a conventional loan and get to use the FHA loan again to repeat.

Characteristically, I choose the 30 year and pay it like a 20, but that extra cash you have to lay out for the 30 doesn't make sense at that loan amount.

The heloc “works” because you are Actually paying more than your scheduled monthly payment every month  You can achieve the Same thing by simply paying extra principal toward your loan. 

In any event, I'm not concerned about it as I'm collecting a little extra to compensate for the inconvenience of her possibly leaving in the middle of winter or something. 

Las Vegas example:Home price $260k, rent per month $1300 (RTV 0.50%)Income $15,60030% down 4% interest mortgage is $898 x 12 = $10,7750.35 % property tax ($902), WAAAY less than 0.5% maintenance ($1300 extra safe), 0.16% home insurance ($435)PM is 8% plus $300 for new tenant.

Then if they want to add a roommate they pay an extra $100? 

If the account gets low then each throws in an extra $5K (or whatever you decide) to boost the balance back up.