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.
Another thing I hate about the eheim is that it needs to be mounded ontop of the tank or sump, so make sure you get some kind of air pump tray. The peristaltic pump can be run with a T right into the canister tubing with a check valve.
Eheim-made aquarium canopies have a cut-out for the Liquidoser, I remember seeing in some photos. But for standard US aquariums and canopies, one has to be innovative in securing the machine otherwise there is a small risk of it dropping into the tank.