The hallmark of this edition is how Anderson approaches the horn. He gives three possibilities: (1) play the alto as a "little tenor," a transposing instrument reading bass clef, (2) play the alto as an alto, reading alto clef and not transposing, or (3)play the alto as a transposing instrument, reading alto clef but imagining the music in tenor or bass and playing the horn as a "little tenor" (i.e. with Bb's and F's in first position).
Each of these approaches has its advantages, but it's clear Anderson was an advoate of the bass clef approach, and the design of the book is clearly laid for that purpose. It's certainly true that the 1st approach is not a long-term solution, as almost no literature is actually written in transposing Eb bass clef. But this is a solid method for the first time alto player as it allows them to quickly gain familiarity with the instrument itself (it's shorter slide positions, smaller intonation adjustments, pitch tendencies, etc.) without being distracted by the need to learn alto clef as well. This can be especailly cumbersome for the tenor player who is learning or still solidifying alto clef on their tenor as well. While a player could easily play any bass clef etude on their alto to do this, the advantage of Anderson's book is that he simultaneously displays the exact same etude on the opposite page in alto clef. So, a player can gain familiarity with a tune reading the bass clef version on the left, and then start switching their eyes to the right hand page to see how that same etude would appear in alto clef. It's an approach David Uber uses in his clef studies books, and Anderson employs it here to assist the player in attaining skill on both (a) the alto trombone and (b) the alto clef as used on the alto trombone. -cdp