While they suck pretty hard until you have somewhat developed a board once that stage is reached they dominate really hard
Either you draw it immediately or sacrifice it to One Jump Ahead
When you summon the Millennium Shield, make sure you have a Shield And Sword Magic card so that you can switch out the shields defense to its attack, giving it a 4000 ATK
Throw as much mana as you can into it, and it provides a solid body that can threaten immediately with haste, ignore chumps with trample, and defend against retaliation thanks to vigilance
Putting aside the avoidance of choosing suboptimal Commanders for archetypes, the lack of pet cards, and never picking cards for flavor, a B4/B5 player is mathing on gameplan and win conditions, and not on what most players could benefit from considering using math for: getting to enjoy the reason you put the deck together in the first place, commonly known as doing the thing