Well, I can see the benefit if you are going to show a layout where there isn't an AC socket supplied to plug your kit into or you don't have a power inverter from 12v or cumbersome generator to hand. People who live "off grid" would have little need as they usually have sophisticated solar panel driven or other means to generate electricity outputted at what one might consider mains AC voltage to power standard household electrical equipment. An interesting niche product for those in power cut prone areas and showing at village fetes or who want to have an interesting diversion from the rigours of that bucket list climb of Mount Everest to hand.
But as the panacea to all outdoor model railway enthusiasts to liberate them from the tyranny of a stepped down fixed point power supply ? I always thought
the real benefit of, at least modern NimH and Lipo, batteries was was the energy density they have and subsequent benefit they offer so that they could be mounted "on-board" negating the need for that tiresome, for some, maintenance of a full layout. Max
My analogue mains powered controller lives indoors and has a, splittable, cable going out of a window attached to the track. It's operated by an RC link. It's called an Aristocraft Train Engineer and you will have to seperate it from my cold dead hands to get me to give it up