put them on my outback 10 years ago. One of the best things I did.
The one downside of the sealevel gauge is that the sensors assume a rectangular tank to determine level. so, more than likely the fresh tank level reading will be spot on. But the black/grey tanks, usually having an odd shape and slope will read somewhat odd. 0% will be empty, 100% near full depending on sensor placement, but in between will be off. What I did was fill the black and grey tanks using a flow meter on the hose and then made a chart showing remaining capacity vs. % readout. As an example, at 50% full on the black/grey was really closer to 30% full.
Install is easy, uses the same wiring as the common KIB system, Mine is the system with 4 tanks, fresh, two grey and black along with a switch for the water pump.