DS. You CAN pay a variable amount each month to clear all outstanding debt on the card, thus attracting zero intrest.
S/O or D/D I can't remember 100%...D/D though iirc.
I know this for fact, as we use a Tesco c/c to buy all our stuff including the weekly shop, (and attract and accrue Tesco points as a consequence to purchase a 'free' trip with Eurotunnel last May) and religiously pay it all off at the end of each month.
If you can hold your hand on your heart and state quite catergorically and honestly to yourself that this is how you will operate your card, you can only be in a win situtation.
I take the point that many get sucked into these cards and offers, only to come badly unstuck when the temptation to over spend creeps in, with the consequential battering of the APR.