What is the difference between the single finger walking labryinth board and the double version? I

The double board is particularly good for aligning the left side and right side of the brain. The single board can provide the same syncing with the left and right side, it just does it while tracing a single labyrinth path instead of two at the same time. For the most part, the choice of a single labyrinth board versus a double board is about personal preferences.