This build mainly works because Mord has quite slow attack speed at lower levels, and hence his damage output early is weak. This fixes that by making him able to trade with burst instead of super long trades like with conq rune trees.

The items are indeed flexible, I really only recommend nashors and hexplate, as these will synergize quite well with hail of blades and his ult.

Speaking of, when you have hexplate online, as well as nashors, you should be saving hail of blades for when you get inside your ult, as the attack speed you'll output is insane. But before then, you can bully the other laner into submission with just nashor components.

For this build you want to be laning against a champ that is 1, weak early game and 2, relies on quick burst trades to win lane. Someone like sett is a good matchup, as he really doesn't fight for super long until late game.

Speaking of ideal, let's go to the opposite, any champs with hard cc, or dashes will counter you hard, unlike mords conq path, cc is quite bad for this rune path, as he needs to be able to proc hail of blades