I'd go for the RSM myself... only coz I have one
Blue screen, batt voltage and all the other stuff gtst-vspec mentioned. top product. I got mine for $360 no G-sensors yet.
you can monitor 4 channels of information aswell, all at once. batt, spead, trip, rev, all that kinda stuff...
and it's got the shift-lite functionality also.. I got a blue LED on the dash that the RSM controls. also has speed alert and a host of other goodies...
some people pay $400 for a tacho with shift light.. the rsm can do it all..
-K.