am also interested in that particular lens. not so many really helpful reviews and opinions out there though. you know there's a cine version, right? and it's only 30$ more: http://www.bhphotovideo.com/c/product/1047004-REG/rokinon_cv12m_m_12mm_t_2_2_cine_lens.html

PV topic on the lens http://www.personal-view.com/talks/discussion/9936/12mm-f2.0-samyang-lens/p1

I had been looking to WD lenses 4 a while and finally got the normal version of the roki 12mm f2 for µFT

 
- Very compact and quite well built, though its shell is mostly plastic OTOH keeps it practical; meaning light
- Mount is one piece of very solid metal, 3 screws... I haven't declicked it yet so can't talk of easiness of op
- Hood and cap are well implemented and no fuzz, 67mm filter thread is just perfect size 4 me
- Focus is easy, 24mm equiv :P, big plastic ring (no rubber) with about 90º throw and around 20 cm minimum FD
- I like how contrasts and renders colours, It is extremely sharp wide open; you can use it f2 with no sweet
- Wide open it can CA's a bit but overall it's super well controlled
- Bokeh (6 blades) is quite ok
- Flare is ok
- Yes it distorts noticeably, but specially for video it is not unpleasing - see Primo distortion and use in cinema
- IMO cuts well with lumix and µFT native lenses - as reference I also have panny 14-140, 20mm pancake and oly 45mm f1.8
 
What I don't like it is mostly related with focus implementation. It focus way beyond infinite #1 (???) - that's very annoying - also the focus ring could be nicer to the touch and a bit more loose/smooth and because asking does not cost anything double the throw. Im my opinion if cinema version fixes specially #1 it's worth it.

Even if not this is a good bong from the brick, I mean bang for the buck =)

Models always at hand and free, well more or less

100% crop screengrab of worst case

 

These images have obviously been edited (colours are not yet 100%, but as examples will do); Fuji 160 Pro style

Salu2 @VK =)