I found out this problem the hard way. Bought one with the smallest diameter shackle I could find, and once I got it out of the blister pack, found it wouldn't fit. Naturally, I couldn't return it.

Gave it to my auto technician, who has an R1100S, an R90/6, a Suzuki 650, and a Honda 250 scoot (and does work on my bike at very reasonable prices). Figured that it was good PR, and that he should be able to make it fit at least one of his fleet.

I heard later that one of the more knowledgeable parts guys at a large BMW dealership (name withheld as a courtesy to protect his or her job) doesn't like them because being in a hurry & forgetting the disk is still locked generally results in a nasty (and costly) surprise.

He added that this occurs more frequently than one might expect. So, given the downside, I figure I'll find other, less effective, ways to secure my bike, and take my chances.