The price is totally fair, IMO. As already said, though, I won't be buying a dumb speedbooster (or a dumb adapter, btw).
What I'd really want, and I'd be ready to spend 300-350€ on it (if well built and decently fast), is a SMART ADAPTER (non speedbooster) for canon glass, so to be able to use a 300-400mm lens for my NX1 and use it with af, aperture and ois.