The mixstirs work very well and can get you to 8 ppm disolved O2, and I have one. Some yeasts like more O2, lager yeast for example, and for those I use 1 liter/min O2 for a minute to get to 10 ppm disolved O2. If you search the achives here, Gordon has said that he uses the mixstrir for most ales, and O2 for big beers.