I called Handi-Quilter in Salt Lake City. The educator for HQ said that you can use whichever thread you choose to use. Whatever you decide you need to be sure to keep your bobbin clean. The recommendation, I have heard, is to clean the bobbin area every other bobbin. I usually brush mine out with each bobbin change and I put oil every other bobbin. Sometimes you have tweak the tension(i.e. loosen tension for Swirls), but I don't have to change the tension when I use Swirls. If I use something like KING TUT then I have to adjust my tension. So, the decision is yours. Do whatever you feel comfortable doing. I just wanted to double check what they told you. I know HQ Educators recommend YLI a lot, but I cannot afford that it.