Patrick.. I have seen the same script material and was a little reluctant to try it.. then again after all the playing around I have done on the SLug.. maybe..
I only have FF running on the Slug. Maybe I am wrong, but it seems to me that the HDD was rarely spun down before when I was unslung to it. Unslung to the flash, the HDD is rarely not spun down except in use.
My FF logs show that it makes a time adjustment of some sort (xxx ticks or whatever) occasionally (probably several times a day) and I think that it wakes up the HDD when it does. I did move the FF log to the flash drive to see if it would help.