Mark, Appreciate the business but the reason I do not sell them is that they do not do what I need them to do for my customers.Its a great concept "free air" but one needs control over how much air and when.Nothing worse than a hot August day no wind and DO levels sinking past 3-4 PPM,its a terrible feeling to see money invested in a windmill with the pond owner having great expectations and you have to tell him he needs to make the wind blow.I prefer to market results and I have not seen that with the mills.I will also tell you that the average pond owner that I have delt with that owns a windmill does not understand his pond and its needs.He saw a mill by a pond and figured it would do the job. The mills are a great visual sales tool. I tell my customers if you want to aerate then aerate and if you want to know which way the wind is blowing then a mill will do that.I have done many DO tests in windmill ponds that had a tough time maintaining 30 40 % of saturation at for example 26 C or 79 F which at sea level in fresh water would be 8.1 PPM DO o 2.5/ 3.5 PPM DO. (not good) most of the time.I have a Koender 1.5 CFM on a 20 ft tower with the original air stone and a Co active airstation valved so that I can switch from stone to station.I use this in one of our display ponds. I like the stone for winter operation as it turns very little water.When there is a situation (no power) then yes they are better than nothing but I have always managed to trench power or air lines to accomodate.Not sure the cost between the old style original mill and the new twin but Im sure the old 1.5 CFM with a Air station will out perform the new style with a stone or any other rubber membrane difusser.I would advise buying one from someone you trust, has parts and a good freight rate and lastly a good price as most of them are priced close together. I would buy one with the airstone and use that as my shallow winter diffuser if ice cover is a concern.Just manifold in an extra valve. If it is not a concern then they make great paper weights and I have a big box of them as we offer a conversion kit for the mills and have replaced many.(sorry bout the long reply)