Do I need external CT or meter during installation?

It really depends on the application. A1-G2 uses CT to do export control, feed-in power calculation and overall power management. BI has two built-in CTs, which are by default responsible for measuring the power to grid port. For whole home solution, there is no need to install external CT, while in some cases for partial home solution, external CT will be needed to make sure that system be able to measure overall power by grid.