Last quarter marketing ran a sign-up bonus: spend $3,000 in the first three months and get $200. New accounts went up 40% and they want to make it permanent. The CRO asks you whether it's actually worth it. What metrics would you look at, and how would you make the call?

市场部上季度推出开卡奖励：3个月内消费满3000美元送200美元，新开卡量比之前涨了40%，他们想把活动常态化。CRO让你评估这个活动到底值不值，你会看哪些指标、怎么判断？