I've used it on the first dozen or more sticks that I cut that weren't already cured. I bought some schedule 40, 5-inch diameter PVC, glued an end cap on the base, and bought a gallon of (expensive) pentacryl at Woodcraft. I placed the PVC tube in a 5-gal. bucket, and screwed an anchor into the sheetrock wall in the garage. Then I secured the top of the tube to the anchor.
I did not conduct any controlled experiments, to compare an stick cut from the same wood under the same conditions, with and without pentacryl treatment.
I left sticks in the pentacryl for a minimum of a month. I can't comment on whether that was appropriate. None of those sticks that I kept or gave to my wife have cracked. I haven't checked with family members regarding their sticks.
Overall, I think the pentacryl likely reduced the shrinkage cracking for the red cedar and several oak sticks.