Like most Magic: The Gathering cards, the value of Portent Tracker depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (March of the Machine)
While you don't have precise control over those options there are still different 8 possibilities of which you do have some control and, most critically, none of which are bad
Without Charizard, this set wouldn't command the $400+ price tag, given that the other chase cards aren't nearly as enticing
Kathari Remnant does have the cascade mechanic, which normally makes me pause a bit about how disruptive free spells are, but with only commons Im not as worried
Sometimes things come really close to actually breaking the game, and those things can be fixed more often than not