Hi nonnon, I am pretty sure this thread should not be used for machine quilting. The description mentions a coating that is used on the thread to prevent knotting when hand quilting; this could sort of scrape off on the eye of your machine's needle and clog it, interfering with your tension. Although thicker thread can certainly be used for machine quilting, especially when you want the quilting to really stand out, I think you would be happier with regular cotton or polyester thread.
I have some Gutermann polyester that does not show any weight...i don't know why! My Gutermann cotton says C Ne 50, meaning 50 weight. Another good brand that you may find at Jo-Ann's is Mettler. The 100% cotton silk finish is nice. It says No. 50 - this is also 50 weight. I hope this helps you! I understand your frustration. Wouldn't it be nice if labeling was consistent across brands? That's why this board is so great, we can help each other!