It works well, its easily understood, and it has enough power to see Modern play as a synergy element
In short, there's plenty of room in Top's corner for it to be both a constant annoyance of organizing and reorganizing cards, and also an extremely powerful, resilient artifact that can be a win-con for an entire deck
Though keeping track of whether a creature is prepared or not could be tricky on the tabletop
I'm not satisfied by my counters, there is not a counter that done both Doom Blade and Go for the Throat 's effects except for Death's Approach (who doesn't make me safety) and Murder (who costs too much mana/swamps in early turns): the best things could be something like Abrupt Decay , with black/blue colors
You can actually choose to pay the kicker cost of two mana, one of which is Black, to allow you to exile any nonland permanent instead