I use a Tailor's Press. I really makes a difference in flat seams. The hammer does work on bulky seams if they are fanned out first. Any hammer will work to flatten but a wood hammer is best and you use it after pressing the seam hot so the wood absorbs the heat super fast and sets the seam. The pricey wood hammers are made from wood that that is used to make the Tailor's Press. It's not just a gimmick, there is a reason.