I love my tailor's ham. I could not press curved seams without it. I also discovered it's a big help when pinning curved seams together. Here are two pieces, one with a convex (hill) curve and the other with a concave (valley) curve.
Even though the seam line is the same length on each, the convex seam allowance is a wider curve so there is more fabric along the it's edge, which means I can't pin by just matching up the seam allowances. But if I drape the pieces over the ham,
the seam line easily slides into place. Neat.
You don't even have to buy a ham. It's the easiest project. Draw an egg shape about the size of an iron, add seam allowance, and sew a scrap of cotton and a scrap of wool together. Leave an opening on the larger end so you can turn the whole thing right side out and fill the ham. I was told they should be filled with saw dust so if you use steam it is drawn through the fabric. I filled mine with with wood bedding material I picked up at the pet store.
Pack, pack, pack it in. And when you think it's full, pack some more. I jammed the wood chips in with a pestle until my hands were sore. But look at this ham.