I use it for piecing all the time. It holds up nicely. I also use it for quilting and it is fine most of the time. However, I apparently got two spools of white thread that came from a bad batch, which had lots of thread clumps in it. That made it very difficult to use. One of these days, I'll call CT to see if they will 'make it good".
Having said that, I have used the CT polyesters in many quilts with absolutely no problems - except for the ususal pilot errors.