P-series compatible polarizers

[mephetic436]

is there a real difference between getting an expensive Singh-Ray polarizer or a cheaper Hitech or Cokin? how significant is this difference if there is one?

[mephetic436]

also is there an important difference between the brands nuetral gray grad or split ND filters OTHER than that they are not EXACTLY neurtral gray...because I can compensate for that in photoshop

[mephetic436]

:/ is this in the wrong section or something?