"A helmet made of glass does not seem useful."
Translation:lI'be'law' 'al'on yughbogh mIv'e'.
I feel more confident about lI'be'law'. It clearly does what it says it does. lI'law'be' relies on negating the entire word lI'law'. The -law' is supposed to indicate that you're fairly sure what you're saying is true, but you're not really trying to say that what you're fairly sure is true isn't true.
In other words, I usually find -law'be' and -bejbe' dodgy, because they're meant to relate the speaker's level of confidence in what they're saying. (-ba', on the other hand, seems to relate what the speaker thinks OTHER people will believe to be true, and -chu' doesn't really involve the speaker evaluating the accuracy of the word.