We'll I'm in the process of sending mine back to Adorama Ebay. I'm having similar issues of extremely bad fringing at larger apertures (1.4 to 2.8) and my copy is really tight to get on and off the camera. So tight I don't feel comfortable putting it back on the camera for fear it may get stuck.
I hope I can get a better copy back as I do like the lens. The bokeh is really nice wide open, not busy but pleasing to the eye IMHO. The focus ring on mines is just right. Just the right amount of friction to make focusing really easy. I've never had a lens this fast so I had a bit of a problem at first with missing focus when shooting wide open and up to F 2.8 with the razor thin DOF but I turned on live view and with the focus peaking feature on the K3 I started getting a lot more keepers. So if you have this problem with your copy shoot with live view turned on and you will enjoy this lens. I really do hope to get a better copy in return.
Oh and I did a little informal test with the Rokinon against my Pentax SMC f3.5 A35-105mm at roughly 85mm. Since they are both manual focus lenses (one prime and one zoom) I thought it would be nice to see the difference. The Rokinon at F3.5 and F8 compared very well against the Pentax. I must admit I really love my Pentax A35-105 so the Rokinon was already in trouble
. Anyway the Rokinon did do better at larger apertures but things evened out as I got closer to F8. Smoother/creamier bokeh at larger apertures but the Pentax colors are hard to beat. I'll let you all know once I get my copy back.