Capital One Financial is a unique player in the bank sector, which will make it a good stock for some and a terrible option for others.Banks are vital financial institutions that facilitate commerce, but not all banks are created equally. Capital One Financial (COF -0.21%), for example, has a unique operating model that can result in material swings in its performance. Here's why some investors will appreciate this large bank and others will want to avoid it.What does a bank do?From a simplistic perspective ...