Well, I happen to actually own one of these cordless things and like it. Use it on the layout to blend scenery with backdrops, and to weather track, structures, etc., without having to lug a hose across finished scenes. It's also handy for little projects like phone booths and lumber loads that don't quite warrant firing up the big guns. It doesn't replace the compressor/airbrush combo, but it does have its uses. Like any tool, match it to the job. And it was pretty cheap, came with its own charging cable and charging is simplicity itself.
Otto