Not only does this provide the Sen Triplets player with additional options, but it deprives an opponent of their own cards
Being able to use two mana right out of the gate is a pretty powerful ability
Normally cards of the Common and Uncommon variety don't go for enough for it to be worth investigating their worth, but when getting into Rare and Mythic cards, especially if they're Foil or any other special variety of card there's a chance that they could be sold for a higher price

Academy Journeymage Acquisitions Expert Aegar, the Freezing Flame Allied Assault Angel of Unity Arcane Epiphany Archmage of Echoes Archpriest of Iona Ardent Electromancer Astrologian's Planisphere Azami, Lady of Scrolls Barrin, Master Wizard Base Camp Benthicore Black Mage's Rod Bloodline Necromancer Blue Mage's Cane Burakos, Party Leader Cascade Seer Champion of Wits Chilling Trap Circle of Power Coastal Wizard Commodore Guff Concerted Defense Cornered by Black Mages Coveted Prize Deadly Alliance Diviner's Wand Docent of Perfection Drana's Silencer Dreamstealer Emeria Captain Ertai, Wizard Adept Expedition Diviner Fever Charm Final Iteration Fissure Wizard Flame of Anor Frostpyre Arcanist Galecaster Colossus Gempalm Sorcerer Ghitu Journeymage Ghosthelm Courier Giant's Amulet Goblin Wizardry Great Hall of the Biblioplex Grotag Bug-Catcher Harmonic Prodigy Harper Recruiter Inalla, Archmage Ritualist Inalla, Archmage Ritualist Inspired Sprite Ixidor's Will Journey to Oblivion Jushi Apprentice Jushi Apprentice Kabira Outrider Kasmina, Enigmatic Mentor Kitsune Mystic Kitsune Mystic Kuja, Genome Sorcerer Lavamancer's Skill Lich Lord of Unx Lindblum, Industrial Regency Lindblum, Industrial Regency Mage's Attendant Malakir Blood-Priest Mana Sculpt Master of Winds Mentor's Guidance Multiclass Baldric

Boreas Charger Despite the mana cost I like Boreas Charger a lot because it can search for lands and get more than one
Many indie TCG creators begin with smaller prototype runs before committing to larger retail quantities