I had an identical offer on my Chase Marriott Premier Visa.

Fortunately my wife & I have transferred all our household spend to her identical card, for Marriott Bonv∘y lifetime status accrual purposes, so I can actually take advantage of this offer.

If one makes any purchases during the duration of the "zero percent" offer, those amounts accrue interest at the normal (high) rate. Trying to "pay off" the new purchases does not work, because the payment is prorated between purchases and balance transfer.

Bottom line: choose balance transfer or purchases, but not both at the same time!