Hi! Thanks for the feedback. I haven't played that much with first strike but it is also a good rune page for mf. If you have positive wr and enjoy playing with it why not.
As for your second question black cleaver's role is to reduce enemies' stacked armour. If they don't have any champs like that or one of your teammates already built it you can choose other options. Such as hyrda or a defensive item according to enemy team's comp.
Also i'll be testing first strike after i'm done with my exam then i can put it on the guide.