The offer is tricky as it is not a 30% bonus offer unless we buy 20,000 or 40,000 miles.
The bonus miles are constant (12,000 miles) for buying miles of 40,000 - 60,000.
If you buy 60,000 miles(i.e. total 72,000 miles including 12,000 bonus), the bonus is only 20%.
CPM comparizon
-buy 40K(total 52K including 12k bonus) : 2.00 ( at $1040.13)
-buy 60k(total 72K including 12k bonus) : 2.14 (at $1542.69)
previous 50% bonus offer
-buy 60k(total 90K including 30k bonus): 2.01 (at $1808.75)