Taken credits like this twice on other platforms and the thing to watch is not the credit, it is what you have to do to earn it.
15% back on spend you were already making is a straightforward discount. 15% back on spend you invented in order to qualify is a 85% loss, and that is the trap every one of these is built around. The monthly cap makes it worse in a subtle way, because hitting exactly $6,667 a month maximises the credit and that number has nothing to do with your business.
Set the budget you would have set, take the credit, ignore the ceiling.