So, does this thing have a alignment lock option? Some key combination like the middle mouse button in g/s/r that allows you to keep the knife level?
Not found anything yet.
When in knife mode, check out your blender status bar. It shows the option.
E for new cut
Ctrl for midpoint snap (between, faces,edges)
Shift ignores the snap
C for angle constraint ( handy for precise cutting)
LMB to define cut lines
RMB to confirm.
Why, yes, there it is! Now how did I miss that, besides the whole “Old, blind, and senile” thing.
Also seems that having verts/edges selected can influence what it does - not sure yet exactly how it works tho. 
lol, we need a proper video tutorial 