So if I lose my job 13 years into my 30 year mortgage, I can just default to what would be my normal monthly payment.
Further, if I'm understanding you correctly, you can "borrow" each month an amount equal to your "extra" monthly payment, with an interest rate equal to your mortgage rate multiplied by one minus your tax bracket, with no closing costs or credit approval requirements.
If you think the prospects for your current job look iffy, you can drop your monthly payments to the base amount while you still have your job, and put that money into a reserve fund. In other words, you pay a little bit extra for the longer-term (on paper) mortgage, but in exchange for that cost you get much more flexibility.