I have a Bernina 200 and when the thread cutter works, I love it. However, 80% of the time it unthreads the needle. My dealer also works in Aurora at Bernina owned Quilter's Resource and when I mentioned it to her she said, "Un, huh." Yes. It does. No help there!
I don't use it when paper piecing b/c I use my #37/1/4" seam foot and you aren't to use the thread cutter with that foot. I have before but don't want to risk it hitting the foot and meeting my eye. I don't wear glasses or safety goggles to sew.