Yeah the Little Stopper isn't yet available in the US, though I've already added my name to the queue at an American supplier. I hope that the wait isn't too long...
During the mid-day's full-sun, I often stack the Big Stopper with other ND filters, even with a second Big Stopper! The ultra-long 8-to-15 minute daytime exposures are a lot of fun to work with! I don't find the blue color-cast of the Big Stopper very difficult to correct in post, even two stacked Big Stoppers are still just the same blue color cast. However mixing different color-casts can quickly become a true nightmare to correct... Now if you really want to see a 10-stop ND filter with a difficult to correct color-cast, you should try the B+W 3.0 (110) filter with the infamous pink-ish brown color-cast! That filter should come with a warning saying "Suitable for Black & White ONLY."