Highly recommended, feeds off of cheap vodka, very little upkeep cost.
I got the medium size for my 90gal system, works great, though the small would handle my fish load. I've got so many fish I can't count heavy feedings, the aquaripure works well. Nitrates used to be at 20ppm a few years ago when I first got it and within 2 months brought it down to zero. You still need separate phosphate control as this doesn't do anything for it.
NOTE: It is possible to feed the effluent from the aquaripure (which is full of white bacteria slime) into a filter of some sort and this in theory will remove their biomass, which has phosphates in it. Personally I feed the effluent into my skimmer/which has a sponge bubble trap, but I don't know how effective this is.