What you're training
A triad's pitch classes don't change across inversions — only which one is lowest does. Root position stacks root-third-fifth from the bottom; first inversion puts the third in the bass; second inversion puts the fifth in the bass. Same three notes, three different foundations. This drill trains you to track the bass note instead of just the chord's overall "color," since that's the one thing that actually distinguishes an inversion.
Two levels, one skill
Level 1 drills a C major triad across all three inversions. Level 2 repeats the exact same three-way question on an A minor triad, so the skill has to transfer — you can't lean on "major always sounds like this" to guess the bass note.
Go deeper
40% of real chords are inverted — the census, playable → shows just how often composers reach for an inversion instead of root position. The theory: inversion → covers the notation and the figured-bass shorthand behind it. Add a fourth note to the stack → is the natural next step, once you can already track a triad's bass note by ear.
Where it fits
Comfortable with chord quality already? Inversions are the same triads you already recognize, just re-voiced — the skill is tracking the bass, not re-learning the chord. The full drill ladder has everything else.