I am sorry I fail to explain the runes but the banshees veil is handy and is more of a situational item whether you have more magicians against you or more enemy melee people.
Then you can decide on your own whether you should get banshees veil or another health item.
Personally i go for banshees veil becuse by near end game u run out of mana quickly and that is a great hinderance. But with the veil you et some magic resist, mana and some more health.

I play Xin Zhao with very high AS and respectable AD but I will maybe try this one out. Only thing I would change is Banshee's Veil for Frozen Mallet, which true, lowers your magic resistance but gives you slow, little damage and more health, which means more damage with Atma's Impaler. But I dont like your masteries, there are no runes and I would change skill order. Write some description and you have +1 from me.