Hi,
I work at a quilt shop that sold Bernina's and we were told to only use Mettler. The shop has since closed and I have done research on the different threads. I teach out of my home now and hava all Bernina sewing machines. I use both Mettler and Gutermann in the machines. One think to remember if you use cotton thread to sew use it in the bobbin too. The Bernina does not like a different thread in the bobbin. Hope this helps.