I have a Taz 6 with the head that now comes stock (the Single Extruder Tool Head v2.1) and managed to get Cheetah printing just fine without this mod.
I have a Ninjaflex sample too so tried using this mod and couldn't get the filament to move even when just trying to load it. Removed the mod and it loaded in ok. Wondering if it's just causing too much pressure, so might re-print it slightly smaller when I get a chance. Trying a test print with the Ninjaflex without the mod, just in case I'm like the 1 person that's lucky enough for it to work!
Also, the new Aerostruder head (Taz 6 and Mini) is now on the Lulzbot store and can handle stiff and flexible filaments - yay!