Ninjaflex might be my favourite 3D filament to print with. It is quite amazing what you can create out of this highly flexible material. We're using it to create ankle bands for the Axivity AX3 accelerometer (there's a how to guide up here for it), but you need to get your settings just right or it turns into a mess of strings. My tips for printing on a Lulzbot Taz 6 with Aerostruder are:
1. Slow the print and travel speeds right down, the slower the better. I print at 15mm/s and travel at 200mm/s.
2. Retract the filament A LOT. I use 5mm retraction, any less can cause issues.
3. I only print it with a 0.15mm layer height. Any higher and I find it can cause issues with print fails.
4. Reduce the temperature. I use 215 degrees Celsius. The default temp is too high and causes stringing for me.
I've attached the curaprofile here.
Another important thing to do - for me at least - is to make sure to do at least 1 cold pull between prints. I find that if the ninjaflex cools down in the head it causes it too jam. I heat the head up to 260 degrees, pulling the ninjaflex out at around 210 degrees and extruding PLA through it at 260 for a second or two and then starting the cooldown to 70 degrees. This is annoying but now I don't get any more jams or problem prints.