I had to do a google search on that, had no idea what you were talking about. Those are for taking cuttings of a plant. Put that around a leaf node, fill it with some growing medium, and hope they root. For a while I was wondering just how strong your painkillers were.
Nope,, never used those. The closest I've come is to purposely bury a section of a limb and put a paver over it. In dry weather toss some water on there occasionally. Worked well on a forsythia.
I'd think your challenge is keeping the moisture level right. Not sure how easy crepe myrtles are to root.
Good luck!