'Tis true that the device is rated for 10-11mm ropes. I'm sure that the Petzl catalog has some kind of skullncrossbones pic for using with smaller ropes.
That being said, it does work with slightly smaller diameter ropes, and I don't remember it being scary at all.
As far as using it with a 9.1, no thanks, not for me.
Cheers.
Jimbo