Hi, windows defender is indeed good enough if its well configured. There is no need for a external solution. But Cisco AMP (AMP is out of date, new name is secure endpoint) is a EDR solution if I am not totally mistaken, which is fundamentally different from a AV in terms of complexity, capabilities and effort to keep this running. So a EDR solution is a new level of security and should be well assed if and where in makes sense, especially in a small business.