Here's my vignette test results. Although I tested the rings at several FLs and apertures, I thought I'd just post 4 of them here for simplicity's sake. I tested both my 17-35/2.8 AF-D with the thickest filter I have (Singh-Ray VND) and the same filter on my 24-120/4.
Really cool idea, but I feel like vignetting would make this system only really useful on 50mil+ lenses. Perfect for a 70-200 or 85 prime, but not so much for a 16-35. Maybe one day! Solid and thorough review though!