biggest problem i have heard with the ninjaflex is getting it to feed. it must be extra soft and rubbery or something. i have used the ecoflex which is the flexible pla. it feeds fantastic but you cant keep it down on the bed which stinks. i am interested to hear some feedback on filaflex or the plastink stuff. i recently had the opportunity to test some very strange material which was a heat meltable silicone. crazy stuff and was just a prototype filament. tricks to get that to feed as well but not impossible. once i got it going i had no issues. there is a fellow member on another forum i am on that has been trying to get ninjaflex to feed for 2 weeks and has still printed nothing. must be really tempermental to the extruder design.