Ok, so my first example of a Lens Turbo on a Panasonic GH3 definitely showed an increase in Field of View. The first tests were purposely setup to show an increase in Exposure, and may have had some lens flare on the overexposed image.
Here's a simple test in a controlled environment shot with a Rokinon 85mm T/1.5 Cine Lens @T/5.6. One is shot with the basic FotoDiox adapter and the other is with the Lens Turbo adapter. I pushed in to attempt to simulate the same framing and keep the chart up to the corners. This adapter does go soft towards the corners, but you decide if it's usable for your needs.
For more info, you can find the Lens Turbo MFT Focal Reducer adapter available now via eBay (click here).
Lens Turbo Focal Reducer Nikon to MFT Micro Four Thirds Adapter