The Third Edition Player's Companion adequately provides additional flair and rules for each player Discipline. Additional flavor information is provided on The Passions as well.
For those desiring to play Earthdawn within the world setting created by the author, this additional material helps focus the player's role play along the intended Discipline lines. For those wishing to create their own backgrounds, tournaments and challenges the additional material is not necessary except for the higher circle discipline rules.
Complete Discipline rules for lower and higher circles should have been included in the Third Edition Player's Guide.
Neither the Player's Guide or the Companion PDFs display properly on an iPad.