nylon is like using fishing line- and when it breaks it is pokey (like those oh so annoying tags in clothes that poke into your skin constantly
the mono-poly invisible threads are not - pokey- they are softer- like thread
you need a less tension- sometimes need to slow down- and use the needle recommended for the chosen thread.
clear is good on light fabrics/smoke on darker fabrics.
if you buy some from Superior threads they will send you a wonderful needle/thread chart that explains what needles to use with what threads-and the sizes for different applications-for free..it is a great resource!