What the metabones adapter does is quite sensible. The image projected by a FF SLR lens covers (for example) 4x the area of a u4/3 sensor. The adapter functions like a reverse-teleconverter, so that the entire FF image is reduced to cover the area of the smaller sensor. By all accounts (e.g. lens rentals) this works extremely well, even with the additional optic elements.
There is no "free-lunch". You are simply using all the light that the lens gathers, rather than throwing it - and the field of view - away.
I understand perfectly well, what the metabones thingy does. And no, it does not "make a NEX a 35mm camera" .. not by a long shot.
And I would not want to fiddle around with exotic thrid-party lens adapters that will always deliver less functionality than original Canon gear and - in the case of the anti-teleconverter will also degrade image quality.
Again, this is me ... others may love it and consider it the greatest thing since sliced bread. :-)
I would much rather take a Canon 100D instead of any NEX or other mirrorless currently on the market, since it has native and full compatibility with my existing Canon EF- and EF-S glass, supporting all of its functionality
What I truly want however is a High End FF mirrorless camera with lens mount. Ideally with the Nikon D800 sensor plus Canon UI and a Canon-adapter for Canon EF- glass ... at a price not higher than the D800. :-)
And if the Sony RX1 had come with a lens mount and a selection of first rate ultracompact fix focal pancakes and an ultracompact, decent kit-zoom ... it would have been the very first camera from Sony ever, to appear on my shopping radar screen. But unfortunately Sony is as stupid as Canon and Nikon regarding their current mirrorless offerings.