Peter, I remember you mentioning the Lucroit set and I went to look at them, the second time in English. I'm experimenting with the Lee and wanted to know more about FotoDiox in particular the filters. The Lucroit system looks interesting because of the way it attaches to a lens. Much more convenient but if the Lee system works for me I'll keep it.
Peter, in my regular work I can usually be a speed demon. I'm used to shooting on a table with an arrangements of lights either ring flash, R1C1 or an array of SB-910's. When I go into the woods for a walk around and find something I would like to photograph it is usually at the wrong time of day. I geotag it on my Garmin thingy and then look around to take a compass heading of the direction I would like to shoot at. I make the notes and calculate the time of day I think would be the best light. I will come back the next day, drop my back pack, set up my tripod, then pour a cup of coffee from my thermos and set up my shot. With that routine I force myself to slow down and take the picture one step at a time. The Lee filter system is a bit more to deal with and I've not found the filter size to be a problem...yet. I just got the Big Stopper and am dying to try it. The Lucroit would appear to be much easier to install and faster to set up but I don't want that. This is why I usually go into the forest or swamps alone or with someone who is willing to work as slow as I am. The entire event to make one photograph could take two hours or more and that is what I'm looking for outside my lab studio.
All in all, what I was really trying to find out was the quality of the FotoDiox filters as they will work with the Lee system and are cheaper.
When you mention the size of the front element of your lenses, presume you're actually referring to the filter thread diameter. There is no direct relationship between the two, though obviously larger front elements tend to require filter threads with a greater diameter.
As an example, the 16-35mm f/4G and 70-200mm f/2.8G II Nikkors both have 77mm filter threads, but the diameters of their front elements (the visible portions) are quite different at 46mm and 72mm respectively.