Bob, I used an even simpler method for my 50mm f1.4
I printed a long black rectangle on a white a4 size paper(Capitol I would do the same trick). I pasted it to a door which was level.
I aligned my tripod and camera at about 2m(7 feet) which I assumed was the most used distance of the lens. In other words, the distance which I though would be most important to my shooting style.
Obviously I didn't have a ruler so I couldn't easily spot if my lens was front focusing or back focusing. I knew that it had a front frocus issue so I just took shots from AFMA 0 to AFMA 20 and I compared the shots on 100% view on my computer. Up till this day it has worked perfectly for me and it only cost me 1 sheet of paper
My 24-105 f4L needed a +4 and my Sigma 50mm f1.4 needed +13. My 70-200 f4L IS was spot on. The 100mm L macro had a different story. It was spot on at 1:1 to 1:2 macro settings, however for portraits it needed a +4 AFMA. Since I rarely used AF during macro, I used +4 on that lens as well.

As far as I'm concerned the Lens Allign couldn't do a better job. I'm pretty confident that I'm no more off than +- 1 which for me isn't a problem at all. With the Lens Allign I'm pretty sure that your method could also cost you +- 1 so in my opinion save the 150$.

Jan