C3 connects the base to ground as far as ac is concerned. Therefore both input and output are connected to the base. (common base amplifier). Current gain is Ic/Ie which is less than 1.
The voltage gain is high since it is Rc/Re. (Approximately the same current flows through them). It is typically 250.
The input impedance is low, typically 20 ohms.
The output impedance is high, typically 1Megohm. The output signal is not inverted with respect the input.
It is often used to match low impedance devices to high impedance ones. It is
commonly used at VHF.