Hi,
The M1 and Dash cannot share the same Ethernet connection. I have one of
these in my car to allow for the laptop to be connected to both devices at the same time. The advantages with these switches is that as the run off of 5V, you can make a power lead that will connect to a USB 2 port and run them from that.*
* Check with you laptop manufacturers details to ensure that the port is capable of powering the device, my experience is that they draw around 150mA in operation with three ports in use, your usage may vary.