Dear lucabutera,
I do appreciate the amount of work you've done, and decided to share with you my experience with speed boosters in order to prevent you from possible future poor sales.
I tried a lot of Metabones. The most important part of any SpeedBooster is how well it performs when a lens set to WideOpen aperture. In two words, all Metabones work acceptable. Some have better Chromatic Aberrations and Sharpness, some performs weaker in this regard.
Also there are number of China adapters on the market, calls Novoflex (if i'm correct with the brand). They call the product NOT a SpeedBooster, but a FocalReducer. They instruct users to Stop Down attached lenses a lot (at least at F5.6-F8.0) in order to get acceptable sharp image.
From my experience, i would never purchase a FocalReducer. We all need WideOpen aperture. And adapter should NOT weaken lens performance when the lens set to WideOpen aperture. That is why we use big lenses and heavy systems. We need Look, Fast apertures + Clear and Sharp images.
I decided to share my experience with you, because it could be unfair if your sales will be lost after such a tremendous amount of work you've done.
All the best.
Ilya