Has anyone used this thread for the top quilt stitching? I'd like some info about it. Seems it'd be the perfect solution to uneven stitch in the ditch technique....no matter how hard I try...some can always been seen! I found it on one site (didn't see it here) and is it nylon and says "as an anchor thread for quilting, or decorative edges and flatlocking with a serger. It is also perfect for "invisible " applique stitching.."

First...what is "anchor" thread for quilt? Top thread?
Second...nylon? I am hating nylon at the moment...okay, polyester not nylon, but they both stretch...is this type of nylon thread stretchy?
Third...life expentancy of the thread?
Fourth ....Seems I'd use this on the top and the fabric matching color on the back...is that right? But then I have two different types of thread...nylon on top and 100% cotton on bottom. I have learned the hard way not to mix cotton and poly fabric...is it the same with thread?

So, please share anything you know about Invisible Thread!