I have one of
these the 85mm version will work in a standard Cokin P adaptor.
I have the 10 stop images do need some white balance correction in PP but the results are pretty good, what stop filter you need depends on where you are shooting i.e. how much light there is in reality you will probably need a selection of different ND filters depending on the situation although the 10 stop will gurantee a long exposure in most situtations although it could be too long.