Regarding operation, no problem, the distribution is ensured ... out of condition back in the head as the signal is duplicated and therefore transits a single image with a single resolution.
Do not confuse so, with small boxes that plug into a USB port and containing a graphics chip allowing you to choose a second resolution, which allows a second display by not duplicating but in addition, and extend your desktop or add a different window to use certain software more ergonomically.
This box is well what is expected, it is advisable to use the second port with a similar screen or video projector that will accept the resolution set by the PC graphics chip for the main screen.