I think serger thread would be fine for FMQ. I use it for most of my sewing, except quilting. I like to piece with the cotton/poly but tried one of the serger-quilting patterns where the piecing is done on the serger. When I pressed the squares, the thread melted and I had to take apart and redo most of them. It hadn't sunk into my pea brain that I can't set the iron on cotton when pressing cotton that was stitched with poly. ALL of my serger thread (3 different brands and yes, one is Maxi-lock) all are 100% poly. I have never seen a cotton serger thread, though it seems like there should be one out there somewhere.