Theres a catch: It must be the top card from your graveyard (yes, Mirage had nonsense restrictions like this)
However, it's effectively providing a consistent card draw, which is essential for control decks , and if you can get it down on turn one, you can activate the card draw ability on your opponent's turn to have eight cards in hand, then give yourself leeway to play two cards per turn and keep activating it for an additional card draw
Was it worth it
Interestingly, the deck's MTG commander Valgavoth, Harrower of Souls doesn't synergize with Great Unclean One at all
No matter, its time to press on
Unlike equipment commanders that only get around equip costs, Nahiri is a planeswalker commander that works well with expensive equipment like Kaldra Compleat and Batterskull