I won’t say anything new by stating that it’s better to have a choice than not to have one. If you think the Samyang 2.8/14 meets your demands you’ll enjoy sharp images that lens is able to produce without spending a lot of money.
Solid casing and good build quality,, Very good image quality in the frame centre,, Good image quality on the edge of the APS-C/DX,, Sensible image quality on the edge of full frame,, Very low lateral chromatic aberration,, Lack of any serious problems with longitudinal chromatic aberration,,...
Some minor problems with spherical aberration,, A bit too high distortion level,, Work against bright light could have been better.