This straightener is small and flexible and quickly welds the bags together.
The advantage of a straightener in front of an iron is that it heats the bag from both sides so the weld is strong and even. In addition, you are less likely to burn yourself on this one than on an iron. Feel free to watch this movie to see how easy it is.
The plates get about 180 degrees hot, which is just right to melt the inner layer of Polyethylene that melts at about 120 degrees, but not too hot so it melts the outer layer of PET that melts at 260 degrees.
It quickly rises to working temperature and is easy to work with.