I understand the cashback calculation but don't understand how the spending bonus works. Have you done the alternate calculation: instead of paying the large fee for govt bill, what happens if you just use the card for your normal fee-free spending and then bank that money in a saving acct paying 1.9%.
Yes , the interest you earn will be less and will slowly build w/ time as you spend but you won't have to pay the large govt fee so perhaps it won't be as bad as you assume.
In the past, the biggest turnoff for these things has been the consequence of not paying back on time. Perhaps you get distracted, ill etc............
