Hmm... I am considering to get this lens.
For the price, I wouldn't complain about the quirks..... could be fun too, depending on how you use the pentagon bokeh and flares.
The vigneting and Chromatic Abberation can now easily corrected with a lot of software during post processing.
My widest M43 lenses so far is the Olympus 8-25 (widest at 16mm) and the 8mm fisheye (which Olympus camera has built in function to defish to 16mm).
The weird thing is that after defish, the view is slightly wider than a 8mm (16mm), which I like.
I also have access to a Sony camera in my household. The alternative is to get the Sony 12-24 F4 or F2.8 but the price is a few times more and it is not even as bright. I would not be worried about not having autofocus as lenses this wide are normally for buildings and landscape and not for moving subjects.