The ElectraScan is an on-board treatment system (legal in our State), which macerates the waste and treats it. It is then pumped overboard (even in the marina, at the dock). We do not have a holding tank. The ElectraScan unit is powered by two batteries. Flush water is raw (from river or ocean). We do not use fresh water to flush. Pretty efficient, this thing!
OF THE HEAD
The big PRO for this unit is of course, that we do not need to deal with emptying the holding tank.
The possible negative side will be when we are out of power (engine "kaputt" and no battery life left) .... then the unit doesn't work.
Eventually we will install a holding tank (another project on the long list of things to do!), between the toilet and the ElectraScan unit, so in case of no power, we can use the holding tank for a while.