Note the basic misunderstanding embedded in that last sentence: Turned off != Hibernated.
While this tool might help you break into a computer you found hibernated, or running while locked, it won't do any good if the power cord is yanked, or the encryption software was intelligently written to only store its key an some volatile memory.
I'm pretty sure that modern hibernate simply stores necessary information from RAM into a file on disk, and shuts off the computer. Then, on boot, it checks if this file exists, and if so attempts to resume from it. So, there is no difference between "off" and "hibernating." The boot sequence will just check if there is a file to resume from.
So, you still need to find a computer that has the volume mounted (either running, in 'sleep' mode with power still being supplied, or from a hibernate file on the disk)