Thanks All for your comments. I finally had a chance to go out and test this thing this weekend and here is my assesment of this cheap alternative:

I took great care in insuring that the target and the camera were carefully aligned---Identical height, perpindicular, Level etc. I ultimtely used a laser level that would shoot across my backyard. I also took great care in making sure camera adjustments were correct, i.e. Wide open aperature (F4), ISO 100, MLU, remote triggered etc.

Using the 500L, I set up at a measured distance of 75 ft from the target. At this distance the target seemed to be almost perfect in that the black and white intersection was just enough to cover the center AF Point and still fully view the ruler along the left side of the frame. Since I was fairly sure my camera/lens combo was front focusing, I shot 10 images at 0, +5, +10 and +15 each. I then uploaded the images into LR for review.

Upon review, My front focusing suspicions were confirmed and this is where it became very difficult to judge. With a depth of field of about 11 inches it was very difficult to tell where the in-focus started and where it ended with any level of accuracy. I also noticed that over the 10 shots, the readings were not consistant so I went with what the majority of shots indicated. Ultimately, I decided that the +10 setting was the closest. Not happy with the lack of accuracy at 75 ft, I moved the camera to 37.5 feet and repeated the test. This became much easier with the depth of field cut to approximately 5 inches. AT this distance I was able to confidently narrow down the settings between +10 and +15. I again repeated the test at +10, +11, +12, +13, +14, +15 (10 Shots each and determined that +12 was my best set---but there was still considerable doubt.

One of my biggest problems wasn't the target but instead, the ruler. It just didn't seem to have enough detail to make assesments that I was confident of.

I haven't tested this with smaller lenses and narrower depth of fields yet, But with long lenses, I am skeptical of this devices accuracy simply because the ruler just doesn't have the detail to make solid judgements.

So, Unfortunately, I don't think my $5 device can provide the level accuracy that the $150 device can, but that it can get you close if you you don't have or are unwilling to spend $150.

I will probably spend the $150 to be confident in my lens accuracy. But, It was certainly worth the effort to explore this alternative.

Thanks again for all your comments.