antonverburg

It can work - but that's all you can say about it. If you are serious about printing ninjaflex, you should use this mod: https://www.youmagine.com/designs/ultimaker-2-straight-tube-flexible-filament-spool-holder. I think it will work on the UM2+ without modification, as the hole locations in the plating of the UM2+ seems to be equal to the UM2.

I have successfully printed several different high-flexible filaments (ninjaflex, semiflex, etc) using my Ultimaker 2. In order to improve print quality I have created a mod that highly improves the quality of the prints: https://www.youmagine.com/designs/ultimaker-2-straight-tube-flexible-filament-spool-holder