Today I received the Big and Super Stoppers and gave them a test drive.
First, I was very surprised there was no light leakage any where on my camera. I kind of figured the Arca body would be perfect, but felt there could be potential of light leakage in the sliding back.
Anyway, I can see the Big Stopper being a huge advantage with the project I bought it for. It took a 1/125 to 8 seconds and made the clouds look nice.
The Super Stopper was overkill and I feel it is going to be more limited in its use. 1/125 becomes 4 minutes according to Lee's chart. The filter does come with a note saying the filter could be off by as much as 2/3 a stop. Consider what 4 minutes gave me, I think mine is closer to 16 stops then 15. Plus, my primary source of over exposure was the clouds. However since they were moving, the highlights never stayed in the same place long enough to be an issue (as fast). I probably could have gotten 8 to 10 minutes without any problems.