@Natey 

Basically the disavantage is that you will have two APs broadcasting the same SSID.  If a client device is between the two APs it may have connection issues such as bouncing between the two AP or not knowing which one to connect to and not connecting at all.  This can typically be fixed by relocating the range extender further away.  Just make sure if you do it is still in a good spot range wise from the host router, otherwise range issues will arise.  

Alternativly if you have an Archer A7 or C7 Version 5 you can enable OneMesh on both the router and range extender and turn these two devices into a Mesh network removing this issue all together. 

@Carl 

New to Mesh, but I'll look into it.

Will a mesh node alter the MAC address of connecting devices like the TP-Link RE220 Range Extender (used in a non Mesh network) does?

I have an A7 1750 and an 1750 range extender, how do I make them into a mesh and can add a second range extender to the mesh?