So unless you're shooting with Nikon G lenses - with no aperture rings - there's no reason to buy the speedbooster other than to minimize the crop factor?
Not saying reducing the crop factor isn't sweet..
BUUUTTT...unless you're shooting with Nikon G lenses, you can just buy some cheap Nikon to MFT adaptor and you're on you way, am I right?
Even if you have a Nikon G lens you don't need a Speedbooster. There are many adaptors out there that can control the aperture of a Nikon G type lens. They are also substantially cheaper than the Speedbooster.
The Speedbooster was designed to increase the FOV of a lens. It also adds a stop of light and sharpens the image as a result.