I have this machine and have used it pretty hard for 26 months.
It is great.
I use it to sew jeans quilts, cotton quilt blocks and to quilt through cotton or polyester batting, too. All types of thread works in it. It is not fussy.
I even used the fancy stitches on my Crazy Quilt seams and to attah laces and trims over the plain seams on my Crazy Quilts.
The main concern I read abut the machine is that it sews oddly, sometimes.
The solution : Re-thread the machine.
As others have said, this clears up the problem.
Susan
NJ