It's the exhaust ability (an exhaust ability can only be activated once, while the card is in play) that makes it really worth looking at
Again, this poses interesting gameplay from both sides, as the player with the Charm has to think whether holding it to try to steal a one-mana permanent in the future is worth it, while the opposing player has to make decisions to play around it e.g
First there was Mangara the Diplomat, and now there's The Gaffer and Dawn of Hope, perfect for any mono-white deck that needs more card draw engines to stay competitive
Verge Ranger While Verge Rangers doesnt directly ramp your mana, it enhances deck consistency
C19 doesnt take away from the fact that, if youre a fan of the format, these decks provide you with a ton of playing pleasure and are definitely worth getting your hands on
Phyrexian Altar is also powerful because its a free sacrifice outlet that can be activated at instant speed as many times as you want