Another little known aspect of the EzyAction (Cheque) accounts is that you can earn up to 300 points per month for maintaining a balance in the account of $1000+ (10 points per $100 up to $3000) - each person is allowed 2 EzyAction accounts and one EzyMastercard so with $6000 in your accounts you can earn 600 points per month. (Admittedly the interest rate isn't great but it isn't bad either for a card/chequebook linked account).
As for the change to earning style - all your accounts have one EzyRewards account so if you open the Mastercard first (or perhaps at any time) you will have Bank Your Points as your earning style even for points earned from EzyAction accounts.
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Andrew's Frequent Flyer Resources