Typically played alongside other artifacts and enchantments to help blunt the opponent's ability to exploit its card drawing symmetry, Howling Mine has been itself a kill card, a lock card, even a precursor to some kind of Storm Seeker
Each of the brackets is intended to represent a different level of play
Gyome, Master Chef is hard to remove and makes the rest of your stuff hard to remove
When you play a modal double-faced card, you choose which face you're playing
I mean, for a start, the level of reselling means it's not all that often you even see packs in stores at regular prices, and as a casual collector, I'm definitely not about to start paying triple or more for them
Most decks need at least a few in their arsenal