I have used invisible thread on the longarm lots of times. I do NOT use the NYLON. It is stiff and feels like fishing line.
I use MONO POLY. I prefer using SUPERIOR MONO POLY and my second choice is using YLI.
You will use a very LIGHT tension when using monopoly. Both companies offer monopoly in clear and smoke.
If you are using this on bright colors, you may want to consider using the smoke color.