Although I personally don't use them (do they even make them for Bernina's?), a friend swears by them. One of her Pfaff's is persnickety about how much thread is on a bobbin, and if she fills a regular bobbin too full, it will almost always have repeated problems until a good bit is gone. In that case, I guess it makes sense.
For me, I just bought a couple of packs of empty bobbins and when I need to fill one, I do several of the same color (unless it's a color I don't often use). I probably do 6 or 7 taupe at a time, maybe 4 each of black and white, and several brown. It doesn't take long and they sit nicely in my bobbin organizer/holder thingy until I need them.