I do! My Ultimaker 2 claims to print with its bowden but I wouldn’t recommend. I have a flexy struder for a modded TAZ and have lots of success! Recent project was for a DIY roof rack air deflector. Laser cut flector, bent aluminum for mounts, and red ninja flex for clamping fasteners!
I use a flexible version from Microcenter, but haven’t used Ninjaflex yet on my Robo3D R1. I’ve made some changes so it feeds better, but it can still jam sometimes if I go full speed (60 cm/s).
I made a cell phone camera mount (the flex grips the phone), and it turned out neat.
I have samples of the material and prints that I have completed. Let me know if you need help check out my hub, it has ninjaflex listed as a option to print.