We're testing a balance transfer offer: the test group gets 0% APR for 12 months and the control group gets 0% for 6 months, with 50,000 emails sent to each group. The PM says we'll just look at application rate and roll out whichever is higher. Do you agree? What metrics would you set for this test?

我们在测一个余额转移优惠：实验组给12个月0%利率，对照组给6个月0%利率，各发5万封邮件。产品经理说就看申请率，哪组高就全量上线。你同意吗？这个实验你会定哪些指标？