The BCW is easy to label and cheap as dirt, and it comes in multiple sizes to fit your collection
Then you sacrifice that copy at the end of the turn
Though exiling four cards a turn sounds like a lot of your deck gone, lets do the math: 100 cards, minus the commander, minus your opening seven-card hand, minus four draw steps by the time you cast this, leaves 88 cards in your library
A few clarifications for those readers who are unsure how Omen Machine (and such similar effects instructing players to cast a card) works: When an effect instructs a player to cast a card ("if able"), and there is no word "may", that means that the player has no choice, and is forced to cast the card, if it can be legally cast
Like recent release Double Masters, players will draft two cards per pick, looking to construct a deck of 60 cards
Stay safe, and keep trading