I bought ninjaflex from 123inkt and I have no reason to be dissatisfied. They delivered on time and the material is running fine.
I agree that different variations is not very convenient, and personally when the diameter is 3mm I wouldn't be to keen on using is. perhaps the first part goes ok, but when you get closer to the core of the reel the curve gets stronger and you get more friction. Also if you deform the filament slightly with your feeder (press it too hard) it can get stuck very easily..
but in most cases you will only have a failed print, and probably some difficulties getting the material out of your bowden tube, because it can be pretty darn stuck sometimes
..(putting it in warm water supposedly helps)