I like the Big Stopper a lot... not only does it give the shutter time I need, it imparts very little colour cast on the image (which is easy to fix with a white balance adjustment). To figure out if it would work for you, you just need to take your normal non-filtered shutter speed and add 10 stops to it. So if your target is a 30 second exposure, then your starting point would need to be no faster than 1/30 second. (30 - 15 - 8 - 4 - 2 - 1 - 1/2 - 1/4 - 1/8 - 1/15 - 1/30 makes ten stops). So if you can use a ISO and aperture combination that would give you 1/30 second unfiltered, under the lighting conditions you are working with, then it's a touchdown.