It comes with the bosch sensor. I found out through some reasearch there is no need to run dual channel, but I am going to have a bung welded in each of the test pipes.
I dont know the difference in the sensors, but the only difference between the M250 and the M300 is that there is a digital readout on the control unit of the 300 (so you wouldnt need a guage) but I wanted the guage, so I saved money buying the 250, but spent extra on the guage