From what I'm reading on Reddit, some are planning on linking a debit card to get the auto-pay discount, but then planning on manually paying by CC before the due date. This way people can earn their points and get the phone insurance as well if their card offers that.
With all the data breaches T-Mobile has had though, I'm not sure about linking my bank account. I may need to figure out a single-use account or something. But this doesn't roll out until May, so I have time.