I recently purchased an AXE300 router. I have RE300 & RE705x range extenders. I am going to connect the range extenders to the router for a one mesh network. 
 

My question is: if I enable Smart connect on the router, will the range extenders also use smart connect or will they have manually switched 2.4ghz & 5 ghz channels for the clients that connect to them? I would like to try smart connect, but I don't want my 5ghz devices to get stuck on the 2.4ghz frequency when they are connected through the range extenders. Or will my 5ghz devices automatically connect to the 5ghz band even though the extender is broadcasting the same SSID for both frequencies?

If smart connect isn't enabled on the extenders and I have separate SSID's for the 2 frequencies on the range extenders but one SSID for both frequencies on the router, will this effect how the devices switch from extender to router(ie will it still function as a mesh network or will it function as a router and range extenders)?

Thanks