Also ninjaflex is NOT pla.

The best flexible pla is polyflex :-)

One thing fffworld you claim:
We have created FlexiSMART to be easy to use by minimizing the problems that the other flexible filaments often have. That is why FlexiSMART can be used in any FFF 3d printer. FlexiSMART has been tested on hot-ends like j-head and all-metal (with and without Teflon) with excellent results.
Which sounds brilliant, but you then say:
The 1.75mm version is more likely to create knots and therefore we recommend to use a special extruder or to modify the one you usually use.
Which is the opposite of the first statement.

So basically it just like all the other tpu filaments out there and a bugger to use in 1.75 diameter.