I have had the Macneil Gloss Boss for the past 7 months and I am pretty happy with it. It has the same rotating brush that Sonny's has come out with, but we have it on electric drive. We are using Black Magic tire dressing with it and have it dialed in to about 0.83 ounces per car. So my current cost per application is about $0.10 per. We are on track to have about 30,000 applications per year.
I looked at all of the different options for tire shine applicators and wasn't impressed with the majority of them, especially the foam ones since the amount of chemical put out is a lot and there is a lot of wastage.
So far, with the Macneil, we have had no maintenance issues (I know, it's still new). It is also very easy to control the amount of chemical dispensed.