I'm on the 2nd week of 2nd phase of this method and love it, I could see myself using Strength Complexes forever. Although sometimes I'm a little tired at the end of the session I typically do all my assistance work then. It's not typically very intense so not horrible to finish.
Like on Shoulder / Squat day after I finish my shoulder and leg complex I'll go do a superset like this:
A1 - Shoulder Shrugs
A2 - Rear Delt Rows
A3 - Lateral Raises
A4 - Front Raises