Is a DLAN adapter with 500 Mbps useful if you only have a 250 Mbit/s contract and how can you get the best possible use out of DLAN? I have Devolo DLAN?

Is a Dlan adapter with 500mbps useful if you only have a 250 MBit/s contract and how can you get the most out of Dlan? I have the Devolo Dlan 500 WiFi.