I have used the Expodisc exclusively for making LCC files and have never been bothered by its questionable vignette. Vignetting is completely adjustable in C1 so if that issue exists it wouldn't be something that would stop me from using the Expodisc.Unfortunately not. It has a vignette all of it's own.
Ditto the LEE circular white lens cap doesn't work (I leave my LEE rings on each lens and use these as the lens caps). It has a circular ring in the centre that makes it unusable for LCC.
Both work well for white balance though
Victor