Ive looked at those as well, I can run them and i was surprised to find out they dont really cost that much more than a standard tach,I wasnt too crazy about how the tachs numbers were laid out because of the display but like that it will display voltage and would free up a gauge spot or two

other than standard oil press,water temp, speedo , tach , fuel level it depends on whats done to boat. if you modified anything water pickup related you might want a water pressure gauge, if you have an electric fuel pump/ aftermarket fuel system might want fuel pressure, I like to have Oil Temp Also. also on fuel or oil pressure always use electric gauges, you dont want to be running oil or fuel at the helm