If i had one of his miners go online for me on 11/5 the suretly amount would have paid by 12/25. After that the income in $ would be $250 every 10 days and dwindling to $22 every 10 days by March. Your contractual payments to them would be more than your income mid-January, and you are on the hook for 5 years of payments. Nothing in that contract says when they will make upgrades and by how much. I fear you may find yourself on the end of a losing battle.
If you had one go online on 11/5 with 1.25THash/s, it would be producing 1.23 bitcoins per day. With the price of bitcoins right now at $440, it would take 20 days to pay off the $8940.00 at the current difficulty. It's been at this difficulty now for 12 days and will probably be 15 days total. You would have the surety paid off a month earlier than your calculations. Right? Am I making an incorrect calculation?
Also, they are required to upgrade the miner with at least 3 new chips every quarter. That actually benefits them because they're taking a 15% cut of the mined coins.