Difficult to use in practice

I practice amateur photography, and have invested in this project to not ruin me.
The quality of the filters is not at the rendezvous. They are not totally gray, and images appear bluish / purple.
Moreover ND4 or ND8 is very low, I thought it was a ND400, the most commonly used, but no.
These filters remove very little light in the end.
Moreover the plastic filter holder is poor, it is difficult to fixed, and there is no manual on how to use it (not easy to fix)
I recommend, as put more in quality gear