Some folks use hacksaw blades, some use a corner edge of a big double cut ba$tard file, and usually they do ok. I've used both to prep glue joints and yes they tear, but I've never had a problem because of it. Then I got a toothing plane, and an extra toothing plane blade (so I don't have to keep removing my only one from the plane body to use by hand) and I never used anything else. Properly sharpened, set, and used, toothing planes cut very clean, AND they level surfaces. They don't tear.
I grind my cores and lams now with 40 grit, so don't need the toothing plane for them, but I always use it to thin and taper bamboo and prep its gluing surface. I generally run the toothing plane mostly parallel with the bamboo's length... but it depends on what I need it to do at any given moment. Sometimes I use it on slight angles as well.
I also use just a toothing blade, held by hand, to prepare gluing surfaces of handle pieces, overlays and such... run parallel... and I'll explain why.
Here's the thing(s) with the toothing plane, and this might explain why the fella mentioned above was seen using it at various angles to the work...
Assuming the blade depth is properly set... if run only in parallel passes, the teeth will tend to run in previous grooves, and cut less and less until they practically stop cutting and the plane will seem to 'float' over the work. That's not necessarily a bad thing, in fact, used as such on a narrow piece of bow wood, you can tell a piece is all leveled off and adequately grooved when the toothing plane quits cuttin'.
If you need to level and/or remove less material, go ahead and run it parallel. If you wish to remove more in one or more areas, and not just groove it to prepare a gluing surface, then changing angles will allow the teeth to cut ACROSS the previous peaks and grooves and continue to remove wood. As with any other, with experience you learn the vagaries of the tool and use it as your needs dictate.
Another thing... they work best when sharpened by grinding their cutting edge in a slighly convex shape. This allows us to better focus our efforts and is especially helpful with backing pieces because, if on the last several passes the tool is ran centered right down the middle and parallel with the piece, it will create a very slight concave and nicely grooved gluing surface from end to end, then when clamped, it flattens out and the glue lines on the edge of the bow are mated perfectly together and are virtually invisible. Sometimes when the bow's done I know right where they're at and I can't find them.
I love my toothing plane and wouldn't be without it.
Tooting planes are best used with glues that have good gap filling properties like epoxies. I use Smooth On. I have never had a toothing plane prepped glue joint fail, including those in working dips and handle areas.
Dean Torges covers the toothing plane's use, care, and even shows how to make one on his dvd, Hunting the Bamboo Backed Bow.
Hope this helps, Zradix.