The Eheim Liquidoser is a well made machine which is useful for daily dosing on, say, vacations. It is reliable. But I suggest you 'practice' with it before leaving it alone to do its duty. Carefully estimate your solution strengths, make sure the batteries are charged enough for the period of use (it does not come with an ac adaptor), and place it in a position from which it cannot be knocked into the aquarium by a passing cat or.... The Eheim Liquidoser is the only low price option for dosing a planted aquarium, as far as I know. Other dosing systems rely on peristaltic pumps, timers and... for more information on those check out some reef aquaria web sites.
Andrew Cribb