If you don't mind waiting 11-13 weeks. a friend of mine popped some which he did not get any keepers out of.... I seriously have never experienced any purplier then my new addition Shoreline, she's almost black.
Sannie says 11-12 weeks, but I've seen journals where people harvested at 9 weeks with fantastic yield, color, and quality. Plus with the F3's, 70+% of successfully germinated seeds will be a purple/blue pheno. Sannie even recommends running it in SCROG as the optimum grow set-up. I am about to pop 4 beans of the Feminized KF myself in about a week, with an undercurrent RDWC setup and scrog. I will definitely be doing a journal.
If you aren't sold yet, check out this smoke report by THE SkunkMunkie:
*Killing Fields f3* (Sannies) ~ Dried & Cured Report
This is a pic of the purple pheno from a journal by The Midnight Gardener on Opengrow. Doesn't get much more purple than that IMHO.
My .02
Chadster152