I have some cheaper, imitation filter holder, in which my polarizing filter, however, does not fit, so I bought the original filter holder. Visually, the original can barely be distinguished from the replicas, but my polarizing filter fits perfectly now.
I find that the most important disadvantage of the Cokin system is the fact that you can not use a lens cap on the filter, which has caused me some problems with dust when I leave my polarizing filter for a long time on the lens.
