There is very few hard and fast rules to quilting, most can be bent or changed to suit the individual,
There is a risk to using the bias, but then as soon as you cut triangle you can't get away from the bias. if the fabric is unwashed and or starched there is less chance of distortion, and if you let the fabric feed through without tugging on it you should be fine, the bonus about being able to change them around is that if you get similar cuts then you can change the look if you are willing to turn the pieces,
I think I read in the book though that you could turn them, though I don't remember specifics on it. And I lent my book to my mom so I can't check on it.