I assume you know that the value of the bond changes as interest rates change and long bonds can be volatile. It is not a riskless trade.
I don't follow. The future changes in price too and is leveraged so added risk. And, pay no interest.
Since this combo is trading in my favour really fast i will close it. Sp500 +100pts (4179 -> 4279) US10y +2.20 (105.25 -> 107.45) Cheers.