Ive printed ninjaflex with the hexagon and a .3mm nozzle.
With direct a feed wades reloaded with hexagon gears.
I had to slow it down to 20mms and play around with the temperature and run it a little hotter.
Keep retraction on but slow it down.
You can put an extra bit of plastic in the extruder below the pinch wheel and hobbed bolt to prevent it kinking there.
I did see an extruder body with this built in but cant find it again.
Theres a new material called semiflex its a little stiffer, maybe this will be better for you.
If your using bowden feed. Youve got no chance.
Gordon