At 2% cashback (5x for Amex) your RM20k bill gives you RM400 per month. Claim laptop after 6-10 months depending how good a one you want. Claim smartphone after another 5 months. Claim vouchers for your grocery/household shopping after that.

Direct cash back means you get 50% less than you would have otherwise. Willing to accept that for convenience?

Wonder what your primary card is until you can think of using 10% cashback card as 'backup'? =p