I plugged my deco into my modems gig port, and then into a tp switch which feds the house with ports!  However the pre plug in wifi speeds were 400mbs reduced to 60mbs! 
 

inculding the modems wifi signal which is independent of the deco, the plugged in computer to a Ethernet port also reduced!!! Took it all out back to normal speeds!  
 

put it into a Ethernet port further down the house and it gives me great speed there, does not interfere with the modem direct or wifi speed!  Weird