without a doubt
Rather an absolute sort of statement. There are always doubts. I use some Lee filters and some Chinese cheapies that cost roughly 5% of the price of the Lee ones.
At my standard output (normally A3+ salon-quality prints from a D800 or D800E) I would defy anyone to discern whether Lee or Chinese had been used.
Of course, you will always get those who are tied to the inane cliché "why spend £1500 on a lens and stick a £5 filter in front of it?". But, when no-one can tell the difference, why not?