This does not replace gdb. It takes gdb - which is an extremely powerful, but also rather low-level debugger - and provides a high-level, simpler, but more convenient UI around it. Under the hood, it still talks to gdb.
This is similar to how VC++ native debugger relates to dbg/windbg. The former is more high-level and easier to use, but the latter is more powerful and lets you do crazy things.