Since the new NiSi 180mm square filter solution for the 11-24mm f4.0 seems to be the only working solution on that lens to go as wide as 11mm without any vignetting (claim by Nisi !) I would like to know if there are already some opinions about this system ? As the whole thing is somehow quite pricy for 3-4 filters + holder at about 1400-1800 USD, I am also quite interested in the general opinion about NiSi filters when compared to other top rated filters (Singh Ray or Breakthrough) for their ND10 and ND6 filters ...