If what you refer to the “backcuts” are what I think they are, then the “shapes” are similar to bon and tan but the energy is different, i.e. bon and tan push forward whereas the backcuts slice back toward oneself.
—Yes. That’s right. The backcuts are similar to bong and tan in the same way that the “diagonal” and the “drilling” punches are similar to bong and tan.
In a land (Australia) whose laws make carrying a pair of big knives for defense completely impractical, I train the butterfly sword form a lot with sticks - you have to use a “bashing” rather than “slicing” energy, as they now become impact rather than edged weapons.
—Yep. Good strategy. I cross-train the bowie techniques with a similar size stick as well. Even the backcuts! 
I train edged weapons too, but combat folder size - I can say I use it for work if challenged, though that would be a difficult argument to use with an 18 inch bowie.
—True. I train with the bowie for many reasons, including its historical value and just the “coolness” factor. It has its place alongside most the the martial arts weapons people train with that are actually directly applicable in modern times…like the butterfly knives, long pole, nunchuku, broadswords, three-section staff, sai, etc, etc. I would dare say the bowie at least retains more applicability that just about any other martial arts weapon because most of its technique can be applied to a large kitchen knife and part of its technique can be applied to a tactical folder.
If WC is meant to practice the pole as a long weapon and swords as short weapons, both being applicable to improvised weapons, you are much more likely to find a blunt instrument lying around than a two foot sword with hook attached in any case, unless you work in a kitchen, slaughterhouse, or operating theatre.
—I agree. But then I hope you are doing most of your stick training with a single weapon. Seldom will you find two blunt weapons of matched length and weight to use like the paired butterfly knives are used.
IMO it’s also important to work with both types of weapons - on one of my Hock Hochheim tapes he warns against allowing knifework to effect your impact weapon training, so that you tend to “slice” with a stick as if it were a blade instead of using proper impact technique.
----Good point.
If those knives are well constructed though, that’s excellent value.
—No complaints so far. 
Keith