The only issue with playing with the top card of your library revealed is that your opponents get perfect information about your draws
C Common Shiranui Squiresaga X FIRE Level 7 [ ZombieSynchroEffect ] ATK 2100 DEF 0 1 Tuner + 1+ non-Tuner monsters You can only Special Summon "Shiranui Squiresaga(s)" once per turn
2004-10-04 Instill Energys untap ability will not untap the creature until it resolves
In addition to the aforementioned drawbacks, it also has the issue of being an Open Construction, meaning that other players can use your Post Office

Darklord Nurse Reficule Dice Jar Dimension Shifter Dinomight, the True Dracofighter Dogmatika Ecclesia, the Virtuous Dogmatika Maximus Dragon Buster Destruction Sword Eater of Millions Eldlich the Golden Lord Fairy Tail Luna Fossil Dyna Pachycephalo Gizmek Orochi, the Serpentron Sky Slasher Gnomaterial Inspector Boarder Jowgen the Spiritualist Knightmare Corurptor Iblee Mahaama the Fairy Dragon Michion the Timelord Necroface Link Apple Pandoras Jewelry Box Performapal Skullcrobat Joker Raphion the Timelord Sandaion the Timelord Sephylon, the Ultimate Timelord Subterror Guru Time Maiden Vanitys Fiend VanityS Ruler Wandering Gryphon Rider Zaborg the Mega Monarch Zap Mustung Zefraath Amorphactor Pain, the Imagination Dracoverlord Blue-Eyes Chaos MAX Dragon Cyber Angel Benten Herald of Perfection Herald of Ultimateness Megalith Phul Nekroz of Unicore Card of Demise Cauldron of the Old Man Chain Strike Dark Snake Syndrome Dimensional Fissure Domain of the True Monarchs Interrupted Kaiju Slumber Kaiser Colosseum Kyoutou Waterfront Nekroz Kaleidoscope Numbers Eveil Pacifis, the Phantasm City Pantheism of the Monarchs Pot of Duality Pot of Extravagance Pot of Prosperity Secret Village of the Spellcasters Sky Iris Terraforming And the Band Played On Anti-Spell Fragrance Bad Reaction to Simochi Banquet of Millions D.D
