There's no fee for using a credit card. I've purchased my annual maximum using my AA credit card.

There's a penalty for cashing in I bonds prior to 5 years ownership. You can't cash them in for six months. I believe you lose 50% of earned interest if cashed in from 6 months to 5 years.

I also buy my nephews savings bonds as birthday and christmas presents, to be used for college. I get the airlines points

The I bonds were at over 7% prior to the current 6-month cycle. 6.49% is still a very good rate.