So what I understood from Kayn

He can be played Both Mid, Top, and Jungle:

For Mid, You'd want to go Shadow Assassin, Since it provides more damage (& Works best against Ranged, which most mid laners are)

For Top, You'd want to go Darkin because it deals Max hp on his ult, and heals him, and provides him with extra cc

I'm guessing there are some exceptions to this, but am i right or way off?