I ended up getting a Symtech BCA-4. The setup was easy, although compensating for the uneven floor was difficult. It appears that my garage floor is rather uneven and no matter how much or how little I rotated the eccentric wheel, I simply could not get the aimer perfectly level. I proceeded to aim the lamps with the aimer as close to level as possible. Adjusting the vertical aim screw on my lamps causes the horizontal aim to change in tandem, so I spent a good little while playing around with both the vertical and horizontal aiming screws. I say "playing" around because the aimer requires you to visually center a white dot to aim the lights. You have to discern the area of highest intensity and then center the dot on the aiming screen in that area.
I tried my best but to be honest, discerning the exact boundaries of the area of highest intensity was somewhat difficult, and it seemed that I could rotate the aiming screws a turn or so in either direction and still perceive the dot as "centered." I suspect that the more expensive models with actual electronics that measure the intensity of the beam would result in a better aiming job.