First, yes this device will work with your router. Second, the difference with the 2 devices has to do with the amount of traffic the device can handle at one time. I don’t have the specs for both products up in front of me, but I know the 705X supports more bandwidth. I suggest seeing what your internet speeds are and then going from there. For example, if your internet speed is only 500mbps, you wouldn’t necessarily need a device that supported extending 2gbps. I found that the 505X was adequate for what I needed.