I use the poly now! Different brands feel like different thicknesses, even though they all say the same.
Have used nylon in the past, but didn't like it. Wonder why some people put it on their bobbins, too!? I always use my "normal" thread for the bobbin. With this new, fine poly I have lowered the top tension a bit and its just like sewing with any thread. Don't have a problem with breakage or anything.
I prefer to use it for hanging, cushions, etc rather than a bed quilt. (All of these "invisibles" can be a bit scratchy.)