They're wonderful to sew with. Some people prefer FMQ with them over their model 15's. I keep meaning to try it someday, but my 27/28 models are buried in the garage at the moment and I've gotten attached to that big class 15 bobbin that I can replace even with a quilt on the machine.
But, I've pieced quilts with the 27/28's. And my little 128 treadle has a picot/hemstitching attachment that produces such a beautiful effect on linen - much easier to control than the 15. That amount of control is great for free-motion embroidery, too - you can sew just a stitch or two, reposition the fabric, couple more stitches, reposition, etc. :)