the triangle papers will be helpful IF you remember all the same things you need to remember if you're making HSTs without them.
when you're done, there's all that paper to tear away. guess how careful you have to be while tearing it away if you don't want to stretch your HSTs out of shape.
save your money.
starch your fabrics.
sew with a scant 1/4".
press carefully.
practicing any new skill is a pain, but well worth it in the end.