There are thread police, just like quilt police. We learn to ignore them.

I use all kinds of thread in my Bernina, including Essential thread. If the teacher had explained that you would get more lint from Essential thread than from some others, then she would be right, but to say that the spool is too loose (when that problem can be fixed) or that the thread is fine for a Brother but not for a Bernina? Please! This would make me take all that she says with a grain of salt.

I have a REALLY old Bernina...the 1008...and all of her life she has been fed whatever thread in the color I needed at the time. She has never refused to use it, she has had only one visit to be serviced and she is clean as a pin. Some of her threads include some that belonged to my Mom and I know are probably 50-55 years old (5-10 cents a WOODEN spool!) but still works well. I've also used every variation of poly and poly-cotton on the market...you name it, I've done it! So I really wouldn't lend much credence to their claims...I too, think she was going for a thread sale!

I agree, thread is thread. Use what works for you the best. Some will have more lint in one machine and very little in the next. Use what works with the fabric you are using. I use a lot of poly threads because I have a lot of it. I use it in my embroidery machine as well as my sewing machines. Works fine. Sounds like the teacher has her preference and thinks every one should use hers only. Take her advise with a big grain of salt!!