I fitted the smart gauge, having fallen for the logic of its makers technical stories,
in particular the inherent faults of the normal battery monitors' (apparent) inabilities to keep track accurately of the sum of in-out current and thus drifting out of phase; and
the ease of fitting.
So far it is a success, in that it appears to do what it is supposed to, but I haven't attempted a serious heavy use control test, and probably won't.
It can only assess the state of charge of one battery or battery bank, but can monitor the voltage of another, say a start battery.
I installed it when fitting a start battery, and now have piece of mind that there is capacity somewhere to start the engine. (The alternator charges the main bank directly, which charges the start battery through a Xantrex slave charger, thus avoiding split charging relays or diodes. Also nice that turning off the 1-2-both switch with the engine running will not wreck anything)
The gauge can be set for all sorts of oltage/capacity alarms which cause the display to flash or come on and I will set mine to activate the display when the batteries are being charged (either by mains or alternator). Note that the display only displays for a short (settable) time.
Happy thus far (and no interest in the company)